icosics

Energy

2011-04-08T11:34:00.003+07:00

Concept of energy

Energy is defined as the ability to do work. Energy takes on many forms and we now discuss the two most basic, kinetic energy and potential energy.

SI unit for energy is joule or J and we can use others as below:
1 calorie = 4,2 joule
1 joule = 0,24 calorie
1 kJ = 1000 joule

Kinetic energy

A moving object can do work on another object it strikes. A flying cannonball does work on a brick wall it knocks down; a moving hammer does work on a nail it strikes. In either case, a moving object exerts a force on a second object and moves it through a distance. An object in motion has ability to do work and thus can be said to have energy. We call the energy of motion kinetic energy, from the Greek word “kinetic”, meaning motion.
We can say kinetic energy is the energy possessed by a moving object because of its motion. A body of mass m moving with a velocity v can do an amount of work, that is:

KE = ½ m v2
Where, KE = Kinetic Energy (Joule or J )
m = mass (kg)
v = Velocity
Kinetic energy is directly proportional to the mass of the object and it is proportional to the square of the velocity.

Potential energy

An object can have energy not only by virtue of its motion, but also by virtue of its shape or position. This is called potential energy (PE).
The most common example of PE is gravitational potential energy. A heavy brick held high in the air has potential energy because of its position. It has the ability to do work, for if it is released it will fall to the ground and can do work on a stake, driving it into the ground. We can say that potential energy is the energy possessed by an object because of its state or position. Let us determine quantitatively gravitational potential energy of an object. In order to lift an object of mass m, a force at least equal to its weight, m x g, must be exerted on it, say, by a person’s hand. In order to lift it to a height h above the ground, figure 1, the work done by the person will be the product of force m x g, and the distance h; that is W = mgh. This work is potential energy of the object. We can write potential energy as:

PE = m . g . h
Where, PE = Potential energy (Joule or J)
m = mass of the object (kg)
g = earth’s gravity (m/s2)
h = height of the object from the ground (m)

Mechanical energy

Mechanical energy is the sum of kinetic energy and potential energy. It is always the same for every position. From the formula of kinetic and potential energy we have:

ME = ½ mv2 + mgh

or

ME = KE + PE
Where ME = Mechanical energy (Joule)
m = Mass (kg)
v = Velocity (m/s)
g = Acceleration of earth gravity (m/s2)
h = Height (m)

As an example, let us consider a stone that is allowed to fall toward the ground. Because it is dropped, it has potential energy equal to m x g x h (we take the ground as the reference level). As it falls, its PE decreases but its KE increases. Just before hitting the ground, it has only kinetic energy. In fact, its KE at the bottom is exactly equal to the PE it had at the top.

The conservation of energy

Whenever energy is transformed, it is found that no energy is gained or lost in the process. We say that energy is conserved. Energy can neither be created or destroyed. Energy can only be transformed from one form into another, and the total amount of energy in a closed system always remains constant. Let us state the law of conservation of energy :
“ The total energy is neither increased nor decreased in any process. Energy can only be transformed from one kind to another, but the total amount remains constant.”

The figure above describes conservation of energy as potential energy changes to kinetic energy. Therefore, no energy lost , it was just changed from one form of energy to another. The various forms of energy include potential energy, kinetic energy, heat energy, chemical energy, solar energy, electrical energy, nuclear energy, geothermal energy and wind energy.

Here are some conversion of energy and the examples of devices:
Electric lamp changes electric energy to light
Firewood changes chemical energy to light and heat
Petrol changes chemical energy to kinetic energy and heat
Loudspeaker changes electric energy to sound
Brake pad changes kinetic energy to heat and sound
Electric fan changes electric energy to kinetic energy and wind energy
Handphone charger changes changes electric energy to chemical energy
Battery changes changes chemical energy to electric energy

Dynamics

2011-01-06T17:40:00.004+07:00

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Classification of Matter

2010-11-20T21:08:00.010+07:00

For this chapter, you can download my presentation here :

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Fundamental Graph Drawing in Science

2010-08-12T21:20:00.008+07:00

Why do we need graph in science?
*Scientific studies involve experiments and collection of data. Data are mere number and can not be used unless interpreted. Graphs are commonly used to interpret data.
*Graphs serve as visual aid to display clearly how two (or more) quantities are related each other in any experiments.
*Sometimes you have to accept uncertainties in experiments due to error in conducting experiments, these can be shown by graph drawing.

What should be found in a graph?
*The common used title is graph of (quantity) against (quantity)
*Basically, there are 2 axes (horizontal axis and vertical axis), it is a good practice to draw the 2 axes, 2 cm from the edge of the graph
Give label of the 2 axes as quantity / unit or quantity
unit
*Scale if necessary, it should be fives or tens.

What you should do
*Always begin from the origin (the point where you start your experiment) for example if you start your experiment at 400C then you have to begin at 400C, do not try to lengthen the line below 400C.
*One axis is for the independent variable, the other for the dependent variable.
*When you plot the graph, make the line or the curve pass through as many points as possible, and draw firmly, do not go over the line / curve again.

So what is gradient?
The value is the division of vertical side with the horizontal side (do not forget its unit).
Gradient will be the constant of the relation of the variables.
From the graph also, we can conclude that degree of X is degree of Fahrenheit, there are still many conclusion can we make by interpreting the graph.

Try below exercise :D

Measurement and Physical Quantities

2010-07-16T08:23:00.007+07:00

Measurement is comparison of one thing with another thing that has already been a standard where an observation is needed. In physics, Measurement is ratio of one physical quantity with another physical quantity that has standard. Measurement is needed in our daily life but sometimes we don’t realize that we have already measured, for example: We know the tallest boy in the class or the most generous person in the school. We can say that almost all occupations need to measure such as a carpenter who will make a shelf or a table and an automotive designer who will make a good design of a car, etc.

Physical quantity is a quantity that can be measured. If it could not be measured, it was not a physical quantity such as sweetness, virtues (discipline, kindness, etc), beauty, wildness, etc. A physical quantity has a SI unit (System International unit). SI Unit is a unit that is accepted by whole countries in the world as a standard unit.

TWO KINDS OF PHYSICAL QUANTITIES
There are two kinds of physical quantities:
1)Base Physical quantities
This physical quantity is very basic and not derived from other physical quantities. There are 7 base physical quantities, as follow :

2)Derived physical quantities
Derived physical quantities are quantities derived from base physical quantities. For example:

STANDARD FORM NUMBERS

Sometimes we can find kind of number which is too long to write for example 1.000.000.000 to simplify we use standard form number as 10^9 or prefix as 1 Giga.

There are some rules to use standard form number :
* The number should have more than two zeros or thousandth up. If it is still hundredth, we don’t need to convert into standard form. See examples below:
100 No need to convert into standard form number.
1.000 10^3
10.000 10^4
100.000 10^5
0,01 No need to convert into standard form number.
0,001 10^–3
0,0001 10^–4
*To convert usual numbers into standard form numbers, we must let the number between 1 - 10. There are two ways to convert according to the numbers, as follows:
a)if the number is more than 1
We count how many zeros that the number has or how many steps we moved the comma of the numbers. See examples below:
-1.000 has three zeros so that we can write as 10^3 in standard form number.
-10.000 = 10^4
-11.000 = 1,1 x 10^4
-27.000 = 2,7 x 10^4
-340.000= 3,4 x 10^5
b)if the number is less than 1
We count how many steps we moved the comma of the numbers. See examples below:
-0,001 = 10^–3
-0,0001 = 10^–4
-0,004 = 4 x 10^–3
-0,0007 = 7 x 10^–4
-0,0025 = 2,5 x 10^–3
*Operation in standard form numbers.
Multiplication
Add the power of the standard form numbers and multiply the numbers in front of the cross sign. For examples:
-10^3 x 10^4 = 10^(3 + 4) = 10^7
-2 x 10^3 x 3 x 10^4 = 2 x 3 x 10^(3 + 4) = 6 x 10^7
Division
Subtract the power of the standard form numbers and multiply the numbers in front of the cross sign. For examples:
-10^8 : 10^3 = 10^(8 - 3) = 10^5
-(8 x 10^9) : (2 x 10^6) = 4 x 10^(9 - 6) = 4 x 10^3

Exercise of Second Semester

2010-05-07T11:05:00.013+07:00

Reflection
1.What are the image characteristics of plane mirror? virtual, upright, same size, laterally inverted

2.Draw a simple reflection!

3.An object was placed between 2 plane mirrors that formed 90. Calculate the amount of images that were formed by the mirrors! State some applications of plane mirror in daily life! 3 images

4.The minimum height of a plane mirror needed to show full image of person with height 2 m is 1 m

5.Convex mirror is also called diverging mirror because it diverges rays of light from a point.

6.Concave mirror is also called converging mirror because it converges rays of light to a point.

7.State the image characteristics in concave mirror! (in each zone)

8.State the image characteristics in convex mirror! virtual, upright, reduced

9.Draw the ray diagrams and for object 10 cm high, placed 40 cm in front of concave mirror with focal length 30 cm!

10.Draw the ray diagrams and for object 20 cm high, placed 60 cm in front of convex mirror with focal length 30 cm!

11.An object 4 cm high was placed 3 cm in front of concave mirror with 6 cm of focal length.
a.What is the image distance? 6 cm
b.What is the magnification? 2 x
c.What is the image height? 8 cm
d.What are the image characteristics? virtual, magnified, upright

12.An object 3 cm high was placed 2 cm in front of convex mirror with radius of curvature 8 cm.
a.What is the image distance? -1,3 cm
b.What is the magnification? 2/3 x
c.What is the image height? 2 cm
d.What are the image characteristics? virtual, reduced, upright

13.How far an object must be placed in front of convex mirror so that a virtual image with half size of the object will be formed if the focal length of the convex mirror is 30 cm? 30 cm

14.How far an object must be placed in front concave mirror so that a virtual image with size 4 times bigger than the object will be formed if the focal length of the mirror is 8 cm? 6 cm

15.Describe some applications of concave and convex mirror in daily life! (based on the characteristics of the mirror)

Refraction
16.Light travels fastest in vacuum with a speed 3x10^8 m/s, but when a light entering a new optically denser medium with a certain angle will cause the speed and the wavelength of light will decrease causing the light bends with direction approaching normal, this phenomenon is also called refraction

17.When light travels from less dense to more dense medium it will bend approaching normal.

18.When light travels from more dense to less dense medium it will bend away from normal.

19.How to know refractive index of medium?

20.A ray of light travels from air to a new medium. A man notices when a light enter the new medium at 60° it will be refracted 45° from the normal line in the new medium.
a.Determine whether the new medium is denser or less dense than air! Explain! denser
b.What is the refractive index and the speed of light in the new medium? 1,5 x 6^0,5 x 10^8 m/s

21.Complete the diagrams to show how light are refracted when it passes from one medium to another:

22.Explain why a swimming pool always appears shallower than it really is while if you see an object from water, it will be further!

23.A swimming pool with depth 2,4 m is seen by a man above the swimming pool. If the refractive index of water 4/3 calculate the depth of the pool that seen by the man! 1,8 m

24.Taking the speed of light in air is 3 x 10^8 m/s and the frequency as 10^16 Hz, the frequency of the light and its wavelength in the water with index of refraction 1,3 will be 1,875 x 10^8 m/s and 10^16 Hz

25.What are the differences between total internal refraction and ordinary refraction? TIR moves from more dense to less dense

26.Explain the terms of critical angle!

27.State 2 conditions for T.I.R to occur! moves from more dense to less dense and its angle is more than its critical angle

28.Pictures below shows a ray of light traveling in 2 different medium: air and glass. If the refractive index of glass is 1,52 and critical angle of glass is 42°, then analyze and complete the path (sketch) for every ray of light below (don’t forget to give reason for your answer)

29.Describe some applications of total internal reflection in daily life! binocular, periscope

Lens and Optical Instruments
30.What are the main differences between lens and mirror? lens refracts light. mirror reflects light

31.Convex lens is also called converging lens.

32.Concave lens is also called diverging lens.

33.State the image characteristics in convex lens! (in all zone)!

34.State the image characteristics in concave lens! virtual, reduced, upright

35.An object 8 cm high was placed 60 cm in front of concave lens and formed a virtual image 15 cm from the lens?
a.What is the focal length of the lens? -20 cm
b.What is the power of lens? -5 D
c.What is the magnification? 1/4 x
d.What is the image height? 2 cm

36.An object 4 cm high was placed 30 cm in front of convex lens with 15 cm of focal length.
a.What is the image distance? 10 cm
b.What is the power of lens? 6,67 D
c.What is the magnification? 1/3 x
d.What is the image height? 4/3 cm

37.Find where the object 4 cm high must be placed in front of a 5 D convex lens, to form a real image with 8 cm high! 30 cm

38.A virtual image with size one third of the object was formed by concave lens with power of lens -20 D. What is the object distance? If the image height is 2 cm, what is the object height? 10 cm, 6 cm

39.Draw the ray diagrams and for object 30 cm high, placed 40 cm in front of concave lens with focal length 30 cm!

40.Draw the ray diagrams and for object 20 cm high, placed 60 cm in front of convex lens with focal length 20 cm!

41.Farsightedness / Hyperopia occurs when the image formed behind the retina. To correct the vision convex lens is used.

42.Nearsightedness / Myopia occurs when the image formed in front of the retina. To correct the vision concave lens is used.

43.A boy with myopia eyes has far point in the amount of 200 cm. If he wants to see objects at distant (very far away) what is the focal length and power of lens he must use so a focus image will formed in his retina? -200 cm, -1/2 D

44.A man with hyperopic eyes has near point in the amount of 50 cm. If he wants to read a book at 25 cm what is the focal length and power of lens he must use so a focus image will formed in his retina? 50 cm, 2 D

45.A boy uses eye glasses with power of lens +2,0 D. (i) Determine whether the boy is myopia or hyperopic (ii) What is the near point of the boy, if the glass is used to read book at 25 cm! hyperopia, 50 cm

46.A student sits at the back of the classroom. First he looks to words written in the board from his chair and after that he looks down to checks the words in his notebook. In the process the shape of his lens is changed as shown in the picture below:
Explain why the eyes’ lens changed shape and what cause it? to expand/reduce the focal length of the eyes so that image will form at retina, when it is used to see close object, lens will be thicker, on the other hand, it will be thinner when it is used to see distant object

47.What are the simmilarities between human eye and camera? it will form real images

48.Where the object must be placed to form a clear image in the camera? What are the image characteristics? anywhere except zone 1 to create a real image

49.Where the object must be placed in front of magnifying glass to produce an image with 4 times magnification if the focal lenght of the lens is 4 cm? 3 cm

50.Type of lens used in magnifying glass is convex lens and the object must be placed in zone 1 to produce an image with characteristics virtual, upright and magnified

51.A photocopy machine is commonly used to produce a copy of document either with the same size or smaller or bigger size. To do that the copy machine also uses convex lens to manipulate the image size. If we want to make copy of a document with smaller size from the original document, where must the original document be placed from the lens? (consider the focal length of the convex lens is 50 cm and the size of the paper is equal with A4 paper, 21 cm x 29,7 cm). Explain and prove your answer by calculation and ray diagram! place the object in zone 3

52.Describe the simillarities and differences between compound microscope and astronomical telescope!

53.A microscope produce 200 times total magnification. If the magnifaction of the objective lens is 20 times, what is the magnification of the ocular lens/eyepiece? 10 times

Matter and Atom
For no 54-56, for each of the following statements, state whether it describes a solid, liquid or gas.
54.The particles move very quickly .... gas
55.The particles are quite close together ... liquid
56.The particles are arranged in a fixed pattern... solid

57.Describe the meaning of melting point and boiling point!
58.Below its melting point a substance will take place in...solid...state.
59.Above its boiling point a substance will take place in...gas..state.

60.Atom is consisting of 3 parts, which are:proton, neutron, electrone

61.Nucleus of an atom in consists of 2 parts, which are neutron and proton

For no. 62-65, states the number and type of atoms that make the compounds below:
62.CO2……………………1 atom C and 2 atom O
63.H2O……………………2 atom H and 1 atom O
64.CH4……………………1 atom C and 4 atom H
65.H2SO4………………2 atom H, 1 atom S and 4 atom O

66.Atom that loss or gained electrons is called………ion

For no. 67-71, classifies the type of changes occur in the process below:
67.Burning paper into ash……………………chemical
68.Dissolving salt in the water……physical
69.Ice melts become water …………………physical
70.Raw egg become hardboiled egg…chemical
71.An apple turning brown……………………chemical

72.8O16, how many protons, electrons and neutrons inside it? 8,8,8
73.11Na23, How many protons, electrons and neutrons inside it? 11,11,12
74.Inside Na+, how many protons, electrons and neutrons inside it? 11,10,12
75.17Cl35, How many protons, electrons and neutrons inside it? 17,17,18
76.Inside Cl-, how many protons, electrons and neutrons inside it? 17,18,18

77.What is the atomic and mass number of the Oxygen atom? 8,16

78.Physical changes are also called………………………… reversible

79.Chemical changes are also called………………………… irreversible

80.Two or more atoms with same number of protons but different number of neutrons are called… isotope

81.Type of bonds when atoms are joined together by electrons sharing is called…… covalent bond

82.Type of bonds when atoms are joined together by electrons transfer is called…… ionic bond

Lens

2010-04-30T08:47:00.007+07:00

The power of the lens equal to reciprocated of the focal length in meter or 100/f for focal length in cm (unit : dioptri/ diopter)
Convex Lenses
Thicker in the center than edges, lens that converges (brings together) light rays.
There are 3 kinds of convex lenses : plan(o)convex, biconvex and concav(o)convex
Concave Lenses
Lens that is thicker at the edges, diverges light rays. There are 3 kinds of concave lenses plan(o)concave, biconcave and convex(o)concave

Ray tracing for convex lens

Ray #1: Light ray comes from top of object; travels parallel to principal axis will be refracted thru focal point.
Ray #2: Light ray comes from top through center of lens is undeviated.
Ray #3 : Light ray comes to the focal point will be refracted to the principal axis
Special for convex lens, we can categorized 5 zone of object and image which simplify us to know the characteristics of the image:
1. Object in zone 1 (from the lens to the focal point) will create image in zone 4 (at the same zone as the object) which means virtual, magnified and upright
2. Object in zone 2 (from the focal point to the 2 times of focal point) will create image in zone 3 (from the 2 times of focal point or more) which means real, magnified and upside down
3. Object in zone 3 (from the 2 times of focal point or more) will create image in zone 2 (from the focal point to the 2 times of focal point ) which means real, reduced and upside down
4. Object in the focal point will create infinity image
5. Object in the two times of focal point will create the image at the same place which means real, same size and upside down.

Concave lens and its ray tracing

Ray #1: Light ray comes from top of object will travelparallel to principal axis will be refracted, as if it comes from the focal point.
Ray #2 : Light ray comes from top of object travels through center of lens will be undeviated.
Ray #3 : Light ray to the focal point will be refracted parallel to the principal axis.

Now compare your ray diagram with below formula

where f for the focal length, s for the distance of the object and s1 for the distance of the image. Do not forget to value virtual image and virtual focal point as a negative value. Then you will find the same result of calculation and diagram. For the magnification you can find by dividing the image distance with object distance or image height with object height.

Lens Exercise
1. Draw the ray diagram when an object was placed in front of convex lens at zone 1
2. Draw the ray diagram when an object was placed in front of convex lens at zone 2
3. Draw the ray diagram when an object was placed in front of convex lens at zone 3
4. Draw the ray diagram when an object was placed in front of convex lens at focal point.
5. Draw the ray diagram when an object was placed in front of concave lens at zone 1
6. Draw the ray diagram when an object was placed in front of concave lens at zone 2
7. Draw the ray diagram when an object was placed in front of concave lens at zone 3
8. Draw the ray diagram when an object was placed in front of concave lens at focal point.

Lensa dan alat optik

2010-04-28T14:54:00.009+07:00

Apabila ada sinar yang datang menuju lensa, maka yang terjadi adalah pembiasan. Ada 2 jenis lensa yaitu lensa cembung dan cekung. Lensa cembung adalah lensa yang mengumpulkan sinar (konvergen) sebaliknya lensa cekung adalah lensa yang menyebarkan sinar (divergen). Sifat dari bayangan lensa cembung sama dengan bayangan di cermin cekung, sedangkan untuk lensa cekung sifat bayangannya sama dengan cermin cembung. Perhitungan yang dipakai pada lensa sama dengan cermin. Jalannya sinar di lensa hampir sama dengan cermin, perbedaannya terletak di pusat lensa. Berikut jalannya sinar di lensa cekung.

Ada 3 sinar istimewa yaitu :
1. Sinar yang datang sejajar dengan sumbu x, akan dibelokkan ke titik fokal yang ada di sisi sumber sinar datang.
2. Sinar yang datang ke pusat lensa akan diteruskan tak berhingga.
3. Sinar yang datang ke titik fokal sisi bersebrangan dengan sumber sinar akan dibelokkan sejajar dengan sumbu x.
Sebagai latihan carilah bayangan yang timbul oleh sebuah benda yang diletakkan 10 cm di depan lensa cekung yang memiliki titik fokal 10 cm. Tentukan pula sifat bayangannya. Nantinya kamu akan menemukan bayangan maya, diperkecil dan tegak.

Sedangkan untuk lensa cembung juga ada 3 sinar istimewa yaitu:
1. Sinar yang datang sejajar dengan sumbu x, akan dibelokkan ke titik fokal yang ada di sisi bersebrangan dengan sumber sinar datang
2. Sinar yang datang ke pusat lensa akan diteruskan tak berhingga.
3. Sinar yang datang ke titik fokal dari sisi yang sama dengan sumber sinar datang akan dibelokkan sejajar dengan sumbu x.

Cobalah untuk mencari bayangan dan sifatnya dari benda yang diletakkan di depan lensa cembung yang memiliki titik fokal 10 cm apabila bendanya diletakkan:
1. 5 cm (sifatnya bayangannya adalah maya, diperbesar dan tegak)
2. 10 cm (sifat bayangannya adalah tak terhingga)
3. 15 cm (sifat bayangannya adalah nyata, diperbesar dan terbalik)
4. 20 cm (sifat bayangannya adalah nyata, sama besar dan terbalik)
5. 25 cm (sifat bayangannya adalah nyata, diperkecil dan terbalik)

Karena sifatnya yang khusus untuk lensa cembung, maka kita dapat membagi daerah lensa cembung sebagai berikut :
1. Jika benda di zone 1 (dari lensa ke titik fokal) maka bayangannya pada zone 4 (area benda) sehingga sifatnya maya, diperbesar dan tegak
2. Jika benda di zone 2 (dari titik fokal ke titik dua kali titik fokal) maka bayangannya pada zone 3 (sisi bersebrangan dengan benda berada di kisaran lebih dari titik 2 kali titik fokalnya)dan sifatnya nyata, diperbesar dan terbalik
3. Jika benda di zone 3 (lebih besar dari titik dua kali titik fokal) maka bayangannya pada zone 2 (sisi bersebrangan dengan benda berada di kisaran titik fokal dan titik 2 kalo titik fokalnya)dan sifatnya nyata, diperkecil dan terbalik
4. Jika benda di titik fokal maka bayangannya tak terhingga
5. Jika benda di titik dua kali titik fokalnya maka bayangannya pada sisi sebrangnya tepat di titik dua kali fokalnya, nyata, sama besar dan terbalik

Sebagai latihan, coba bandingkan hasil gambarmu dengan formulanya.

Untuk mencari tinggi bayangan bisa menggunakan perbandingan tinggi bayangan dengan tinggi benda atau jarak bayangan dengan jarak benda (atau merupakan nilai perbesaran) Apakah hasilnya sama? Jika tidak mungkin kamu masih salah dalam menggambarkannya.

Mata manusia adalah salah satu contoh lensa cembung. Mata dapat diubah menebal atau menipis untuk dapat melihat benda dengan jelas. Benda harus diletakkan di ruang 3 (lebih dari 2 kali titik fokal) supaya bayangannya dapat ditangkap retina dengan baik, untuk itu ketika melihat benda yang jauh, lensa akan menipis, sebaliknya untuk melihat benda yang dekat, lensa akan menebal.

Sifat dari lensa juga banyak dimanfaatkan sebagai alat optik. Ada 2 jenis alat optik, yang dipakai berhubungan langsung dengan mata atau memerlukan medium untuk dapat dilihat mata. Akan tetapi semuanya memiliki fungsi yang sama yaitu membantu manusia untuk melihat segala sesuatu lebih jelas. Untuk yang berhubungan lengsung dengan mata harus menghasilkan bayangan maya, karenanya bendanya harus diletakkan di zone 1. Contoh alat optik ini :

-Kacamata minus (lensa cekung)
Orang yang rabun jauh (myopia), bayangannya jatuh di depan kornea mata, untuk itu diperlukan lensa cekung sehingga bayangan jatuh di kornea.
-Kacamata plus (lensa cembung)
Orang yang rabun dekat (hypermyopia), bayangannya jatuh di belakang kornea mata, untuk itu diperlukan lensa cembung sehingga bayangan jatuh di kornea. Bila rabun jauhnya karena usia (presbyopia), juga diperlukan lensa cembung.
-Lup (lensa cembung)
-Teleskop
Menggunakan 2 lensa cembung yang pertama disebut lensa objektif yang akan menghasilkan bayangan di titik fokal lalu bayangan ini menjadi benda untuk lensa okulernya. Hasil bayangannya haruslah maya supaya dapat dilihat mata.
-Mikroskop
Menggunakan 2 lensa cembung yang pertama disebut lensa objektif yang akan menghasilkan bayangan di zone 3 lalu bayangan ini menjadi benda untuk lensa okulernya. Hasil bayangannya haruslah maya supaya dapat dilihat mata.
-dll...

Jika alat optiknya menggunakan medium maka bayangan yang timbul haruslah nyata, lalu oleh medium layar atau kertas atau lainnya dapat dilihat oleh mata. Contohnya :
-Proyektor
Umumnya memperbesar hasil bayangan, jadi benda diletakkan di zone 2
-Kamera
Dapat memperbesar hasil bayangan tapi umumnya sama besar
-Mesin fotokopi
Dapat memperbesar atau memperkecil hasil bayangan tapi umumnya sama besar

Pembiasan

2010-04-26T13:49:00.007+07:00

Pembiasan adalah suatu peristiwa pembelokan sinar karena adanya perubahan medium seperti gambar berikut (perubahan medium terlihat dengan adanya perubahan warna).
Jika seberkas sinar dari medium yang kurang padat ke medium yang lebih padat, yang terjadi adalah pembelokan sinar yang mendekati garis normal (dari medium putih ke medium hijau), sebaliknya jika sinar datang dari medium yang lebih padat ke medium yang kurang padat maka yang terjadi adalah pembelokan sinar yang menjauhi garis normal (dari medium hijau ke medium putih).

Secara matematis perubahan sudutnya dapat diformulasikan sebagai n1 sin i = n2 sin r dimana n1 adalah refractive index medium asal, i adalah besar sudut datang, n2 adalah refractive index medium yang dituju dan r adalah besar sudut yang dibelokkan. Semakin besar refractive indexnya maka semakin padat benda tersebut.

Selama pembiasan, frekuensi tidak mengalami perubahan, tetapi kecepatan dan panjang gelombang berubah mengikuti persamaan n1 v1 = n2 v2 (untuk kecepatan) dan n1 lambda1 = n2 lambda2 (untuk panjang gelombang).

Khusus pembelokan dari medium yang lebih padat ke medium yang kurang padat, ada kemungkinan terjadi pemantulan (Total Internal Reflection) apabila sudut datangnya melebihi sudut kritis. Sudut kritis adalah sudut datang yang akan menghasilkan sudut belok sebesar 90. Sebagai contoh apabila sudut kritis sebuah gelas 41, maka apabila sebuah sinar datang dari gelas ke udara dengan sudut kurang atau sama dengan 41 yang terjadi adalah pembiasan, tapi apabila sinar datangnya memiliki sudut datang yang melebihi 41, maka yang terjadi adalah pemantulan. Perhatikan gambar di bawah dari kiri ke kanan. Ketika sinar datang dari gelas adalah 30 maka sinar tersebut akan dibelokkan menjauhi garis normalnya di udara. Ketika sinar datang dari gelas sama dengan 41 maka sinar tersebut akan dibelokkan sebesar 90. Tetapi, ketika sinar datang sebesar 45, yang terjadi adalah pemantulan di dalam (total internal reflection).

Pemantulan dan Cermin

2010-04-23T10:50:00.009+07:00

Pemantulan sinar adalah peristiwa kembalinya sinar dengan sudut pantul yang sama besarnya dengan sudut datang pada bidang yang sama (sudut alpha = sudut beta).
Sudut datang adalah sudut yang mengapit antara sinar datang dengan garis normal (garis yang ditarik tegak lurus dari perpotongan sinar dengan bidang pantul).

Ada 2 jenis pemantulan yaitu pemantulan yang sempurna (regular reflection) apabila pemantulan terjadi pada bidang yang rata, pemantulan yang tidak sempurna (diffuse reflection) apabila pemantulan terjadi pada bidang yang tidak rata, banyak lubang ataupun relief lain.
Pemantulan yang sempurna terjadi pada cermin datar ataupun bidang yang halus dan mengkilap sebaliknya pemantulan yang tidak sempurna bisa terjadi pada cermin cembung ataupun cekung.

Untuk itu, perlu beberapa istilah untuk membedakan kedua bayangan yang mungkin timbul, yaitu :
1. Bayangan nyata yaitu bayangan yang tidak dapat dilihat oleh mata, untuk dapat dilihat oleh mata diperlukan proyektor (contohnya bayangan yang ditimbulkan dalam bioskop memerlukan layar supaya dapat dilihat oleh penontonnya. Bayangan ini terletak di depan cermin.
2. Bayangan maya yaitu bayangan yang dapat dilihat oleh mata dengan jelas contohnya adalah bayangan yang kita lihat apabila kita berkaca. Bayangan ini terletak di belakang cermin.
3. Bayangan diperbesar
4. Bayangan diperkecil
5. Bayangan yang sama besar
6. Bayangan tegak apabila posisi benda dan bayangannya sama
7. Bayangan terbalik apabila posisi benda dan bayangannya tidak sama (terbalik)
8. Divergen atau menyebar
9. Konvergen atau memusat
10. Terbalik secara lateral, jika kita mengangkat tangan kanan, di cermin yang terlihat kamu sedang mengangkat tangan kiri

Ambillah sebuah cermin dan perhatikan bayangan yang timbul. Bayangan yang timbul adalah bayangan maya, tegak, sama besar dan terbalik secara lateral. Pemantulan di cermin datar akan menghasilkan bayangan maya, tegak, sama besar dan terbalik secara lateral. 2 cermin datar bila diletakkan berhimpit dan membentuk sudut, akan menghasilkan bayangan-bayangan, karena 2 cermin datar saling memantulkan satu sama lain dan dapat membentuk lingkaran, karenanya jumlah bayangan yang terbentuk dapat dihitung sebanyak (360 / sudut yang dibentuk ) - 1. Sebagai contoh jika 2 cermin datar membentuk sudut 90 maka jumlah bayangan yang akan timbul di depan 2 cermin tersebut adalah 3 buah.

Jika kita berkaca di depan cermin cembung atau cekung, bayangan yang timbul bisa bermacam-macam karena permukaannya tidak menentu. Pada cermin cembung dan cekung ada titik pusat kelengkungan dari kurva cembung aatu cekung (center), selain itu ada titik fokus yang berjarak separuh dari titik pusat dan cermin tersebut. Apabila kita berkaca di depan cermin cembung, maka bayangan yang timbul adalah bayangan maya, diperkecil, tegak dan terbalik secara lateral. Hal ini dapat kamu lihat pada kaca spion, kaca pada perempatan jalan, kaca yang ada di supermarket untuk melihat apakah ada yang mencuri atau tidak.
Sebelum kita mengetahui jalannya sinar di depan cermin cembung/cekung, kita perlu tahu bagian-bagian dari sebuah cermin cekung/cembung.

Berikut adalah jalannya pembentukkan bayangan di cermin cembung.

1. Sinar yang datang lurus sejajar akan dipantulkan ke titik fokus
2. Sinar yang datang ke titik pusat akan dipantulkan melalui titik pusat juga
3. Sinar yang datang ke titik pusat akan dipantulkan oleh kaca sejajar dengan sumbu x

Jalannya sinar di cermin cembung berlaku juga di cermin cekung.

Cobalah menggambarkan apabila posisi benda sebagai berikut :
1. Antara cermin dan titik fokus
2. Titik fokus
3. Antara titik fokus dan titik pusat
4. Titik pusat
5. Lebih besar dari titik pusat

Pasti sifat bayangannya berbeda kan? Jika gambarmu benar maka kamu akan memperoleh :
1. Bayangan maya, diperkecil, tegak dan terbalik secara lateral
2. Tak terhingga (sangat jauh)
3. Bayangan nyata, diperbesar, terbalik dan terbalik secara lateral
4. Bayangan nyata, sama besar, terbalik dan terbalik secara lateral
5. Bayangan nyata, diperkecil, terbalik dan terbalik secara lateral
Dari sifat yang timbul maka dapat diringkas bahwa khusus untuk cermin cekung, maka kita dapat membagi daerah cermin cekung sebagai berikut :
1. Jika benda di zone 1 (dari cermin ke titik fokus) maka bayangannya pada zone 4 (belakang cermin) sehingga sifatnya maya, diperbesar dan tegak
2. Jika benda di zone 2 (dari titik fokus ke titik pusat) maka bayangannya pada zone 3 (lebih besar dari titik pusatnya)dan sifatnya nyata, diperbesar dan terbalik
3. Jika benda di zone 3 (lebih besar dari titik pusat) maka bayangannya pada zone 2 (antara titik fokus dan titik pusatnya)dan sifatnya nyata, diperkecil dan terbalik
4. Jika benda di titik fokus maka bayangannya tak terhingga
5. Jika benda di titik pusatnya maka bayangannya pada titik pusatnya, nyata, sama besar dan terbalik

Selain dengan cara gambar, adapula formula untuk mencari bayangan yaitu

dimana f adalah panjang titik fokus ke cermin, s adalah jarak benda ke cermin dan s1 adalah jarak bayangan ke cermin. Jika sifatnya maya (bayangan maya ataupun titik fokus yang maya) maka nilainya negatif, sebagai contoh cermin cembung memiliki titik fokus yang maya dan bayangan maya, maka dalam perhitungan diberi nilai negatif. Untuk mengetahui tinggi bayangan dapat menggunakan nilai perbesaran yaitu perbandingan antara tinggi bayangan dengan tinggi benda atau perbandingan jarak bayangan dengan jarak benda.
Silakan dibandingkan hasil gambar dengan perhitungan ini, tentunya harus sama besarnya.

Exercise on Wave n Vibration

2009-11-07T07:30:00.008+07:00

1.A source of vibration that vibrates in the air has a wave length of 34 m. If the speed of wave is 340 m/s, then what is the frequency of the vibration?

2.A source of vibration produces 600 vibrations in 1 minute. Calculate the wave length produced if the speed of wave in the air is 340 m/s?

3.Frequency of a turning fork is 200 Hz. Calculate the wavelength that produced if the speed of wave in the air is 340 m/s?

4.What is the period and speed of wave for a wave that has frequency 2 kHz and wavelength 17 cm?

5.A wave travels at 50 m/s. If the wavelength is 2 m, what is the frequency and period of the wave?

6.A wave travels 35 m in 5 s. What is the frequency and period of the wave if the wavelength is 0,5 m?

7.The length of radio wave is 500 m. What is the frequency of the wave if the wave travels at speed of light in vacuum?

8.Sketch the shape of transverse wave that travels for 6 s with frequency 0,5 Hz and 2 cm of amplitude.

9.

The wave above is showing a distance of 30 m in 3 seconds.
What are the frequency, period, amplitude and speed of the wave?

10.2 crests and 1 trough of wave are produced in 1,5 s.
a.What is the frequency of the wave?
b.What is the period of the wave?

11.

The picture shows a wave that travel at 80 cm/s in 5 seconds
a.What is the wavelength of the wave?
b.What is the amplitude of the wave?
c.What is the frequency of the wave?

12.Observe the picture below:

If the frequency of the wave is 30 Hz and the distance traveled is 150 m
a.What is the wavelength of the wave?
b.What is the speed of the wave?

13.A piece of cork floats above sea water. The cork moves upside down 100 times in 40 s. In the same time the sea wave has travel 60 m. what is the wavelength of the wave?

For questions no. 14 and 15

14.What is the frequency and period of the wave?
15.What is the amplitude and speed of the wave?

Wave

2009-10-22T13:19:00.009+07:00

Gelombang adalah getaran periodik yang dapat memindahkan energi.
Contoh gelombang laut adalah getaran periodik air laut yang memindahkan energi kinetik, gelombang radio adalah getaran periodik yang memindahkan energi suara, dan lainnya.
Jenis - jenis gelombang adalah gelombang transversal dan gelombang longitudinal.
Ketika gelombang terjadi ada dua gerakan yang terjadi yaitu gerakan gelombang (rambatan) dan gerakan getarannya. Gerakan inilah yang membedakan gelombang longitudinal dan gelombang transversal.

Kalau diperhatikan, gelombang ini bergerak dari tengah ke sekitarnya, hal yang sama terjadi pula pada getarannya bergerak dari tengah ke sekitarnya. Gelombang yang arah rambatannya sama dengan arah getarannya dinamakan gelombang longitudinal. Contoh gelombang longitudinal adalah gelombang suara dan gelombang per. 1 gelombang longitudinal harus memiliki satu rapatan dan satu renggangan.

Gelombang ini bergerak / merambat dari kiri ke kanan dengan arah getaran naik turun, jadi arah rambatan dan getarannya tegak lurus. Gelombang ini dinamakan gelombang transversal contohnya adalah gelombang tali, gelombang radio dan gelombang air laut. 1 gelombang transversal harus terdiri dari satu bukit dan satu lembah.

Gelombang mempunyai beberapa karakter untuk membedakan satu gelombang dengan gelombang lainnya, yaitu:
1. Frekuensi yaitu banyaknya gelombang dalam satu detik, jadi jika radio bergetar 98.7 MHz maka radio tersebut memancarkan 98.7 mega gelombang dalam 1 detik
2. Periode yaitu waktu yang diperlukan untuk sebuah gelombang merambat, jadi jika sebuah gelombang bergerak 5 Hz berarti ada 5 gelombang dalam 1 detik dengan demikian untuk 1 gelombang butuh waktu 0.2 detik, jadi periodenya adalah 0.2 detik
3. Panjang gelombang adalah panjang rambatan sebuah gelombang.
4. Amplitudo adalah jarak maksimum atau minimum dari sebuah gelombang ketika ia bergetar.
5. Kecepatan gelombang adalah perbandingan jarak yang ditempuh gelombang dan waktu tempuhnya.

Dari gelombang transversal diatas terlihat bahwa ada 1.5 gelombang dalam waktu 6 detik dan menempuh jarak 30 m. Dengan demikian frekuensi gelombang tersebut adalah 1.5 gelombang / 6 detik atau 0.25 Hz, periode gelombang tersebut adalah 6 detik / 1.5 gelomabang atau 4 detik, panjang gelombang adalah 30 m / 1.5 gelombang atau 20 m, kecepatan gelombang adalah 30 m / 6 s atau 5 m/s dan amplitudonya 6 cm.

Gelombang memiliki 4 sifat yaitu :
1. Pemantulan (refleksi), apabila gelombang yang sedang bergerak terkena rintangan, maka gelombang tersebut akan berbalik arah (pemantulan) contoh yang paling sering terlihat dalam kehidupan sehari-hari adalah gema yang merupakan pemantulan dari gelombang suara ketika gelombang tersebut mengenai sebuah tembok.

2. Pembiasan, hal ini terjadi apabila sebuah gelombang berbelok akibat adanya perbedaan medium getarnya sebagai contoh pensil didalam gelas yang berisi air akan terlihat seperti bengkok, hal ini terjadi karena gelombang cahaya mengalami perbedaan medium dari udara ke air sehingga gelombang cahaya akan berbelok sehingga terlihat seakan-akan pensil tersebut bengkok.

3. Superposisi, hal ini terjadi apabila 2 gelombang bertemu, 2 hal yang mungkin terjadi adalah kedua gelombang tersebut menguatkan satu sama lain atau melemahkan satu sama lain.
4. Difraksi, terjadi apabila sebuah gelombang mengalami perbedaan arah gerak karena memasuki daerah yang lebih sempit.

Secara umum gelombang dapat dibedakan menjadi 2 yaitu gelombang mekanik karena membutuhkan media untuk bergetar dan gelombang elektromagnetik karena dapat bergetar meskipun tidak ada medianya. Keunggulan lain dari gelombang elektromagnetik adalah kecepatannya yang sangat besar yaitu 300.000.000 m/s. Gelombang elektromagnetik adalah gelombang transversal dan terbagi menjadi 7 macam, yang membedakan adalah panjang gelombang, frekuensi dan energinya. Energi tertinggi adalah untuk gelombang yang memiliki frekuensi tertinggi. Jenis gelombang ini secara urutan panjang gelombang adalah:

1. Radio adalah gelombang yang terpanjang dalam gelombang elektromagnetik dan banyak dipakai untuk siaran radio atau televisi.

2. Micro banyak dipakai untuk komunikasi dan pemanas makanan (microwave)

3. Infra Red banyak dipakai untuk remote control dan deteksi panas tubuh

4. Visible adalah satu-satunya gelombang elektromagnetik yang paling jelas dilihat oleh mata kita, merupakan sinar yang kita lihat setiap hari memiliki warna merah, jingga, kuning, hijau, biru, nila dan ungu

5. Ultraviolet dipakai untuk membunuh kuman dan virus, sumber terbesar dari matahari. Dipakai juga untuk pertumbuhan karena UV memacu pertumbuhan vitamin D

6. X Ray dipakai untuk kedokteran, mendeteksi tulang dan gigi atau bagian lain yang tidak dapat tembus oleh sinar X

7. Gamma adalah gelombang terpendek dari gelombang elektromagnetik dan diperoleh dari reaksi radioaktif, banyak dipakai untuk dunia kedokteran seperti mengobati kanker ataupun untuk sterilisasi

Thermal Physics II

2009-10-02T12:12:00.004+07:00

Jika sebuah benda dipanaskan, yang terjadi adalah :
1. Benda akan mengembang
2. Benda akan bertambah panas (suhunya bertambah)
3. Benda akan berubah bentuknya (es mencair, air mendidih, dan lainnya)

Kalor jenis adalah ukuran banyaknya panas (kalor) yang dibutuhkan untuk menaikkan suhu sebuah benda, secara matematis dapat ditulis
Kalor jenis = kalor yang dibutuhkan / beda suhu yang terjadi
Untuk memanaskan 1 kg benda akan lebih kecil dibandingkan 5 kg benda, untuk itu dibutuhkan terminologi kalor jenis apesifik yang merupakan banyaknya kalor yang dibutuhkan untuk menaikkan suhu untuk sebuh massa benda, secara matematis
Kalor jenis spesifik = kalor / (beda suhu x massa benda)

Kalor laten adalah ukuran banyaknya panas yang dibutuhkan sebuah benda untuk berubah bentuk. Macamnya kalor laten adalah kalor lebur dan kalor didih. Secara matematis dapat ditulis
Kalor laten = kalor yang dibutuhkan / massa benda

Untuk menggambarkan kebutuhan kalor, ada baiknya digambar terlebih dahulu grafik suhu terhadap waktu seperti berikut :

Dari gambar terlihat bahwa pada bagian kuning, benda berbentuk padat, sehingga yang terjadi adalah perubahan suhu (kalor jenis yang berperan dalam kebutuhan panas), begitu juga untuk yang berbentuk cair (hijau telur asin) dan gas (abu-abu).
Pada bagian mencair maupun mendidih, tidak ada perubahan suhu hanya perubahan bentuk. Saat ini yang berperan adalah kalor laten. (hijau untuk bagian mencair dan biru untuk bagian mendidih).

Jika ada 2 benda, 1 lebih panas dari lainnya, maka yang lebih panas akan memberikan kalornya kepada yang lebih dingin sehingga suhu air akan sama atau dengan kata lain
Kalor yang dilepaskan = kalor yang diterima
Contoh air panas 70C jika dicampur dengan es, es akan mencair dan suhu akhir air dan es tersebit antara 0C dan 70C

Kalor tidak dapat diciptakan ataupun dihilangkan, hanya dapat berpindah, prinsip berpindahnya kalor dibedakan menjadi;
1. Konduksi yaitu perpindahan kalor antara partikel satu dan lainnya dalam sebuh benda contohnya panci yang dipanaskan akan menjadi tinggi suhunya. Contoh konduktor adalah logam.
2. Konveksi yaitu perpindahan kalor karena adanya aliran kalor contohnya air yang dipanaskan, air yang panas akan naik ke atas, lalu yang dingin akan turun ke bawah (sehingga akan terkena kalor juga.
3. Radiasi yaitu perpindahan kalor yang dapat terjadi meskipun tidak ada mediumnya (hampa udara) contohnya panas matahari dapat berpindah ke bumi meskipun melalui ruang hampa udara di luar angkasa. Radiasi dapat ditolak dengan menggunakan benda berkilau.

Thermal Physics I

2009-10-02T10:57:00.008+07:00

Semua benda jika dipanaskan akan mengembang dan jika didinginkan akan menyusut.
Besarnya pengembangan dan penyusutan tiap benda berbeda, secara umum pengembangan / penyusutan benda berwujud gas paling besar bila dibanding cair dan padat, begitu juga pengembangan / penyusutan benda berwujud cair lebih besar daripada padat. Karena perbedaan inilah, maka dibutuhkan koefisien pengembangan benda baik secara linear (panjang), luas maupun volume, yang mana untuk tiap benda besarnya berbeda. Sebagai contoh koefisien pengembangan air lebih kecil daripada udara.
Besarnya pengembangan dan penyusutan tergantung pula oleh ukuran awal dan selisih temperature (suhu) akibat didinginkan maupun dipanaskan.
Secara matematis dapat dituliskan sebagai berikut :

Air mengalami pengembangan dan penyusutan yang berbeda pada suhu 0C sampai dengan 4C. Bukankan es memiliki volume yang besar daripada air? Karenanya air jika didinginkan dari 4C ke 0C, air tidak akan menyusut tapi justru pengembangan sebaliknya dari 0C ke 4C air justru mengalami penyusutan. Inilah yang dinamakan anomali air. Apa kerugian dari anomali air dalam kehidupan sehari-hari?

Sifat pengembangan dan penyusutan dapat diaplikasikan untuk berbagai hal. Termometer dalam penunjukan skala suhunya memanfaatkan sifat ini, ketika masuk ke pengukuran yang panas, cairan yang ada dalam termometer akan mengembang dan menunjukkan suhunya, begitu pula jika pengukuran dingin, cairan yang ada akan menyusut untuk menunjukkan suhunya.
Contoh lain dari pemanfaatan sifat ini adalah keping bimetal. Keping ini terdiri dari dua logam yang berbeda sehingga bila dipanaskan akan mengembang dengan jumlah yang berbeda sehingga akan menyebabkan pembengkokan ke arah yang terkecil pengembangannya.

Exercises on Thermal Physics I

2009-08-10T12:26:00.004+07:00

1.The length of mercury thread of an unmarked mercury thermometer at ice point is 20 mm and the length of the thread at steam point is 120 mm. Determine:
a.What is the temperature in °C when the length of thread is 110 mm?
b.What is the length of the thread when the temperature is 20°C?

2.The length of mercury thread of an unmarked mercury thermometer at ice point is 14 mm and the length of the thread at steam point is 164 mm. Determine:
a.What is the temperature in °C when the length of thread is 44 mm?
b.What is the length of the thread when the temperature is 60°C?

3.A piece of wire with initial length 3,2 m gain length of 1,6 cm when the temperature rise in the amount of 300°C. What is the linear coefficient of the wire?

4.The length of a metal at 0°C is 1 m. If the linear coefficient of the steel is 25 x 10-6 /°C, then what is the length of the metal at 50°C?

5.A piece of metal has length of 5 m and being cooled from 100°C to 0°C. If the linear coefficient of the metal is 0, 000012/°C then what is the final length of the metal?

6.A piece of copper gain length of 0,076 cm if the temperature rises in the amount of 10°C. If the linear coefficient of the copper is 0, 000019/°C, what is the initial length of the copper?

7.The length of steel at 50°C is 60,03 cm. If the length of the steel at 0°C is 60 cm then what is the linear coefficient of the steel?

8.Volume of liquid X at 20°C is 200 cm3. Calculate the volume of liquid X if it’s being heated to 120°C. (γ liquid X = 0,0002/°C)!

9.A steel tank with 3 liters capacity was filled up. Then the steel tank was heated for 1 hour so the temperature of the tank and liquid A is uniform. Consider the rise of temperature of the tank and liquid was the same, 100°C, determine:
a.Will the liquid A spill out of the tank?
b.If yes, calculate the volume of the spill water!
(γ liquid A = 0,00021/°C ; α steel = 0,000012/°C)

10.Josh is building his own thermometer with his own scale (Josh degree). He decided that the temperature of melting ice in his scale is -10°Josh and the temperature of pure water steam is 90°Josh.
a.Find the conversion formula between Josh scale and Celsius scale!
b.If the in Josh thermometer is read 30°Josh, what is the scale in Celsius?
c.If in Celsius scale is read 70°C, what is the scale in Josh scale?

11.If the temperature in Fahrenheit scale show the same number in Celsius scale multiply by three (°F = 4 x °C) what is the temperature in Celsius scale?

12.Two pieces of railroads made of alloy steel will be joined together. Each of railroads is 10 m long at 30°C. If the maximum temperature at daylight can reach 40°C, calculate the gap between railroads so they have enough room to expand at daylight! (α steel = 0,000011/°C).

Optical Instruments

2009-04-30T12:04:00.024+07:00

Optical Instrument

Eyes
Eyes are convex lens because they have to create real image to hit the retina so that we will be able to see objects. To see distant object, the lens will become thinner hence to see close object, the lens will become thicker, thus enable the object to be placed in zone 3 to create a reduced image in our retina.
Our eyes are able to see object or virtual image.
To see how the light comes to our eyes, visit :
http://www.ziddu.com/download/4536270/Howlightcomestoeye.pps.html

Optical instruments can be categorized into 2 types that is connected to eyes or other medium. The one which is connected to eyes should create a virtual images because our eyes only receives virtual images. Consequently, the one which is connected to medium should create real images.

Here are the examples that created virtual images:

Concave Lens
Nearsightedness (myopia) can not see distant object, to help them, we use diverging lens because diverging lens will make distant object become closer object. Their eyeball is too long, image focuses in front of retina. It will expand the focal length so the image will be focused in retina.

Convex Lens
Farsightedness can not see near object, to help them, converging lens is needed to make a further image that can be seen by farsightedness. Their eyeball is too short, image focuses behind retina. Convex lenses shorten the focal length. It also helps presbyopia which eyeball is too short because of age, image focuses behind retina

Cylindrical lenses
It is used to help astigmatism – irregular curvature of retina so image is blurred
Cylindrical lenses reduce the irregular to focus the object

Telescope
Telescope is used for seeing distant object. Virtual image should be formed in front of the telescope so that we will be able to see the object. Telescope contains at least 2 lens, one is used for the objective lens (near to the object) and the other for eyepiece (near to our eyes). The focal length of the objective lens should be bigger than the eyepiece due to the object distance. Therefore, the power of lens of the objective lens is smaller than the eyepiece.
Normally for the objective lens, the converging lens is used to converge all the light, to make a clearer image.
When the light of the distant object comes to objective lens, the image will be formed on the focal point of the objective lens. he created image will be an object for the eyepiece.
Eyepiece can be made by using both convex or concave lens, because both lens will create virtual images. However the concave lens will diminish the object, which will make us hard to see the object.
To create virtual images in a convex lens, object should be placed below focal point, this will lead to the maximum length of telescope as an addition of focal length of objective lens and eyepiece.
To create virtual images in a concave lens, object can be placed anywhere however the results are varied but in general is reduced image.
The magnification of a telescope can be calculated as focal length of an objective lens over focal length of an eyepiece.
Meanwhile, the maximum distance of a telescope is an addition of focal length of objective lens and eyepiece.

Microscope
Microscope is used for magnifying tiny object. Virtual image should be formed in front of the microscope so that we will be able to see the object. Microscope contains at least 2 lens, one is used for the objective lens (near to the object) and the other for eyepiece (near to our eyes). The focal length of the objective lens should be smaller than the eyepiece due to the object distance. Therefore, the power of lens of the objective lens is bigger than the eyepiece.
The lens that is used for microscope is convex lens, because the main idea of microscope is to magnify object, which only can be done by convex lens.
For a maximum magnification of microscope, the object in front of objective lens should be placed in zone 2 (so it will create a real and bigger image in zone 3 for the eyepiece). Then, the object for the eyepiece should be placed in zone 1 so that a virtual and magnified image will be formed.
Magnification of a microscope can be calculated as a result of magnification of objective lens times by magnification of the eyepiece.

Magnifying Glasses
Magnifying glasses or loupe is used for magnifying object. Virtual and magnified image should be formed, that's why convex lens is used.

Examples that create real images are:
Camera
The principle of camera is the same as eye because the image should be made at the back of the lens (real image). In that case, camera should use converging lens (convex). The object should be put over 2F because film / negative in camera can handle a reduced image not a magnified image. The further the object, the focal length of the camera should be longer too (we can achieve this by reducing the power of camera lens or forwarding the lens to the object). The real image will be projected to photographic paper or camera screen which enable us to see a picture. It can be used to magnify the image too.

Diascope / projector
Created image is real and magnified.

Photocopy machine
Created image is real and same size, however it can be used to magnify and reduce objects too, depends on the position of the lens. To magnify means we place the object in zone 2, hence, to have a reduced image, we should place the object in zone 3, etc.

Matter and Atom

2009-03-16T09:17:00.009+07:00

All matter is made up of elements.
There are 92 elements that occur naturally. The elements hydrogen, carbon, nitrogen and oxygen are the elements that make up most living organisms.
Matter has mass and takes up space.
Atoms are basic building blocks of matter, and cannot be chemically subdivided by ordinary means.The word atom is derived from the Greek word which means indivisible.
Atoms are composed of three type of particles: protons, neutrons, and electron. Both the protons and neutrons reside in the nucleus.
Protons is positive charge, neutrons have no charge and electrons (reside in orbitals around the nucleus) is negative charge.
Protons and neutrons are responsible for the atomic mass (mass number) while the number of protons determines the atomic number.
To know the atomic number and mass number, we can check from periodic table, for example 6C12 means the atomic number is 6 (it has 6 protons), mass number is 12 (it has 6 neutrons).
For exercise : find atomic number and mass number of Freon, Helium, Oxygen, Barium.

The number of protons in an element is constant (e.g. Hydrogen only has 1 proton) but neutron number may vary, which will lead to varied mass number. When the same element may contain varying numbers of neutrons (mass number) ; these forms of an element are called isotopes. Carbon, with atomic number of 6 can have 6, 7, or 8 neutrons (Carbon 12, Carbon 13, Carbon 14)
The chemical properties of isotopes are the same, although the physical properties of some isotopes may be different. Some isotopes are radioactive, they "radiate" energy as they decay to a more stable form.

A condition of which the number of neutron are the same for two elements (which have different atomic number) are called isotones. For example Boron 12 and Carbon 13

When mass number of two elements are equal, we called these elements as isobar. For example Boron 12 and Carbon 12.

Exercise : find isotopes, isotones and isobar of Barium and Calsium

A compound is a stable neutral group of at least two element in a strong bonding.
An ion is an atom or compound which has lost or gained one or more electron.
A mixture is a stable neutral group of at least two atoms or compound in a weak bonding that can separate easily (mostly by physical action).

Exercise : which one molecule, compound, ion, mixture of following :
1. Water
2. Alcohol
3. Acetone
4. Syrop
5. Juice
6. Acetic acid
7. Urea (fertilizer)
8. Urine
9. Cheese
10. Cake

Atomic bond is a strong bond that can not be separated unless a chemical action occurs. There are 2 kinds of atomic bond :
* Ionic bond is a bonding for a positive charged ion to a negative charged ion (usually a bonding consists of metal and nonmetal element, e.g. salt / NaCl)
* Covalent bond is a bonding for nonmetal element e.g. water

Exercise : which one the ionic bond and covalent bond
1. Salt
2. Acid
3. Amonium
4. Lactic acid
5. Nitrogen Compound
6. Base
7. Sugar
8. Rhizobium

Physical changes due to pressure and temperature which will result as a changing of texture, shape, size, color, mass, weight, and density without disturbing the bonding of the components.
Physical changes are reversible, means after they occurred, they can change to the former condition, e.g. shaping log into toys

Physical processes that were trigged by pressure are:
* Filtration uses some apparatus such as filter (paper) and tunnel e.g. to separate sand from seawater
* Injection e.g. to form plastics bead into plastics tray
* Chromatography is a separation of stationary components by moving the other components to other direction e.g. to separate black into its components
* Sedimentation takes a longer time to settle all the bigger density material e.g. water sedimentation from the sand and other deposits
* Centrifugation takes a short time because of the rapid centrifugal force e.g. to separate blood cell from its plasma by centrifuge

Kind of physical processes that were trigged by temperature are :
* Evaporation e.g. to separate salt from salt solution
* Crystallization use heat to separate due to the difference of the boiling point e.g. to crystallize candy
* Distillation use heat to separate due to the difference of the boiling point e.g. to separate kerosene from oil

Chemical changes due to pressure, temperature etc and will lead to changing of bonding. This changes can be observed as a result in gas (bubble), sound (explosion), odor, heat, form (burning), precipitate, decomposition of components.
Chemical changes are irreversible, means after they occurred, they can not be changed, e.g. fermentation of cassava will create lactic acid.

Refraction

2009-02-05T08:36:00.027+07:00

Simple refraction or bending of light can be observed by watching the apparent depth of a pool is shallower than its depth.
When light comes to the different medium, the light will be bent.
When light from less dense media come to more dense (denser) media, the light will be bent approaching the normal line ( i > r ).
When light from denser (more dense) media come to less dense media, the light will be bent away from the normal line ( i < r )

Law of Refraction
1.The incident ray (i), normal and the refracted ray (r) all lie in the same plane.
2.For two particular media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant (sin i/sin r = constant = n =refractive index) or mathematically
n1 sin i = n2 sin r
1 refers to where the incidence ray comes and 2 refers to where the refracted ray comes.
The refracted index for air, usually taken as 1

Refractive index also can be calculated as V air / V medium
When we see through a pool, its depth will look shallower, by knowing its refractive index, we can calculate the apparent depth as n = real depth / apparent depth

Work Example of Refraction

State whether this statement true or false
1. The light comes from the air to the water can be bent up to 30 degree depends on the angle of incidence.
2. The light comes from the denser medium to the less dense medium will be bent away from the normal line.
3. The shining diamond occurs because refraction.
4. Total internal reflection only occurs when the angle of refraction is bigger than critical angle.
5. Rainbow is a sample of dispersion due to different medium of light transmission during rain
6. Calculate and sketch the ray from air to plastics (refractive index 1.5) as below
7. If the incident ray comes with the frequency of 1014 Hz then find the frequency, wavelength and speed of the refracted ray

Total Internal Reflection
When the light travels from the denser medium to a less dense medium, the light will be bent away from the normal line. As the angle of incidence is increased further, it will reach the critical angle ( angle of incidence which will create angle of refraction value as 90 degree ). Consequently, when the incidence light reach over the critical angle, total internal reflection will occur. For example, by taking the normal critical angle of a glass is 41 degree, we can know that when the angle of incidence light less than or equal to 41 degree,refraction will occur, on the contrary, total internal reflection will due. Observe the figure below from left to the right, when the angle of incidence is 30 degree(less than its critical angle), the light will be refracted away from the normal line. When angle of incidence equal to critical angle, the light will be refracted as far as 90 degree. Last, when the angle of incidence is 45 degree (more than its critical angle), the light will be reflected inside the medium (total internal reflection).

Total internal reflection can be seen in a optics cable, the benefit of using total internal reflection is that it will transmit quickly and clearly.

Light and Mirror

2009-01-10T08:01:00.029+07:00

What is Light?
As atoms absorb energy, electrons jump out to a higher energy level.
Electrons release light when falling down to the lower energy level.
Photons - bundles/packets of energy released when the electrons fall.
Light as stream of photons

Color of Light
1. Transparent Objects
Light transmitted because of no scattering
Color transmitted is color you see. All other colors are absorbed.
2. Translucent
Light is scattered and transmitted some.
3. Opaque
Light is either reflected or absorbed. Color of opaque objects is color it reflects.
White light is the presence of ALL the colors of the visible spectrum.
Black objects absorb ALL the colors and no light is reflected back.

Light and its Sources
Luminous object
Luminous objects have their own light example : sun, firefly, light worm
Hence, non luminous objects reflect light example : moon, hand
Incandescent light
Light produced by heating an object until it glows.
Fluorescent Light
Light produced by electron bombardment of gas molecules
Phosphors absorb photons that are created when mercury gas gets zapped with electrons. The phosphors glow & produce light.
Neon light
Neon inside glass tubes makes red light.
Other gases make other colors.

Reflection of Light

Reflection – Bouncing back of light waves at the same angle (angle of incident = angle of reflection or α = β) and same plane. The green dashed line is showing the normal line to help us identify the angle of incident (the angle between the incident ray and the normal line) and the angle of reflection (the angle between the reflection ray and the normal line), the normal line should be perpendicular to the plane.
Kind of reflection :
1. Regular reflection – mirrors smooth surfaces scatter light very little. Images are clear & exact. 2. Diffuse reflection – reflected light is scattered due to an irregular surface.

Exercise :
1. Draw the reflection of the light when a light enter at the angle of 20 to the plane
2. Draw the reflection of the light when a light enter at the angle of 45 to the normal line

Term of Image / Shadow
Real Image - Can be projected onto a screen because light actually passes through the point where the image appears , always inverted
Virtual Image - “Not Real” because it cannot be projected, image only seems to be there
Upright – Image' position is the same as the object
Inverted – Image is upside down.
Laterally inverted – Image is right side left
Enlarged – Image is larger than actual object.
Reduced / Diminished – Image is smaller than object.
Converge / Converging – Bring the light to a point

Diverge / Diverging – Diverge the light to many points.

Principal Axis – Base line through the center of a mirror or lens
Focal Point – Point where reflected or refracted rays meet & image is formed
Focal Length – Distance between center of mirror/lens and focal point
Centre Point – Centre point of a mirror or lens

Plane Mirror – Perfectly flat
Image is virtual, laterally inverted
An angled mirror will create number of shadows as (360 / α) – 1 where α is the angle. For example two mirrors when placed to create an angle of 90 will give us 3 shadows

Convex Mirror (Diverging Mirror)
- Curves outward, virtual focal point.
Image is virtual, laterally inverted, reduced, upright, closer than it appears
Use: Rear view mirrors, store security

Ray #1: Light ray comes from top of object will travel parallel to principal axis is reflected as if it come from focal point.
Ray #2 : Light ray comes from top of object to the center of mirror will be reflected back.
Ray #3 : Light ray comes to the focal point will be reflected to the principal axis
Exercise :
Find the image and its characteristics by drawing and calculating in front of convex mirror with the centre point of 5 cm when the object is placed
(1) 8 cm in front of the mirror
(2) 3 cm in front of the mirror
(3) 1 cm in front of the mirror

Concave Mirror (Converging Mirror)
Curves inward, real focal point.

Ray #1: Light ray comes from top of object will travel parallel to principal axis will be reflected to focal point.
Ray #2 : Light ray comes from top of object travels through center of mirror will be reflected back.
Ray #3 : Light ray comes to the focal point will be reflected parallel to the principal axis
Exercise :
Find the image and its characteristics by drawing and calculating in front of concave mirror with the centre point of 5 cm when the object is placed
(1) 8 cm in front of the mirror
(2) at the centre point of the mirror
(3) 3 cm in front of the mirror
(4) at the focal point of the mirror
(5) 1 cm in front of the mirror
If your drawing is right, you will find the characteristics as (1) real, inverted and reduced (2) real, inverted and same size (3) real, inverted and magnified (4) infinity image (5) virtual, upright and magnified

Therefore we can conclude, special for concave mirror, we can categorized 5 zone of object and image which simplify us to know the characteristics of the image:
1. Object in zone 1 (from the mirror to the focal point) will create image in zone 4 (at the back of the mirror) which means virtual, magnified and upright
2. Object in zone 2 (from the focal point to the centre point) will create image in zone 3 (further than its centre point) which means real, magnified and upside down
3. Object in zone 3 (further than its centre point) will create image in zone 2 (from the focal point to the centre point ) which means real, reduced and upside down
4. Object in the focal point will create infinity image
5. Object in the centre point will create the image at the same place which means real, same size and upside down.

Now compare your drawing (the place of your image) with the formula:
1/f = 1/s + 1/s’ where f is focal length and s is distance of the object and s’ is distance of the image
M = h’/h = s’/s where M is magnification and h is height of the object and h' is the height of te image. When magnified, the value of M is more than 1. Then if it is reduced the value is less than 1. Last, if the value of M is 1, it means that the image has a same size as its object.
Both should show the same place, or it means that there is something wrong with your drawing or calculation.

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Exercise of First Semester

2008-11-25T13:09:00.015+07:00

Thermal Physics I

When you are asked to design a container of liquid, what factors should you consider in designing? Give reasons and calculate the volume of container to hold 5 L of liquid

Are rail pad made as one piece long or pieces? Give reasons

If you are asked to design a thermometer for measuring the temperature of boiling water, which liquid (beside alcohol and mercury) is the best? You can find the supporting data by yourself

Thermal Physics II

Are wooden house hotter than cement house? Give reason

Explain how convection related to land breeze

A 500 watt heater is going to boil 2 kg of -5 C ice, how long will this process take? Draw the heating cooling graph, if necessary

1 kg of -5 C ice will be immersed in 1 kg of boiling water. What will be the final temperature?

Wave

What is the type of wave and how many waves are formed from the picture below?

If total time taken is 20 seconds and total length of the wave is 100 cm, calculate the frequency, period, wavelength, speed of wave and amplitude!

What is the type of wave and how many waves are formed from the picture below?

If total time taken is 15 seconds and total length of the wave is 30 cm, calculate the frequency, period, wavelength, speed of wave!

State 4 behaviors of wave!

What are the spectrums of EM wave? Which spectrum has the shortest and the longest wavelength? Which spectrum has the highest and lowest frequency?

Sound

The range of audibility of human ear is between _________ to ___________
The sound with frequency above the range of audibility of human ear is called_______________ while the sound with frequency below the range of audibility of human ear is called_______________

Sound needs ___________ to travel and it travels fastest in _______________, followed by_____________ and the slowest in __________________

A boat transmits sonar pulse to the bottom of the sea and receives the echo 1,5 s after the transmission. If the speed of sound in the water is 1.500 m/s, then calculate the depth of the sea.

A gun is fired between two parallel vertical walls. The echo from one wall is heard 1 s later. The echo from other wall is heard after 3 s later. How far apart are the walls if the speed of sound in air is 340 m/s?

Sketch some transverse to show voice with:
a.high and low pitch
b.Loud and weak sound

Merssene’s law investigates the relation between frequency string with length, area, density and tension of string. What will happen if:
a.Longer string is used?
b.Thinner string is used?
c. Denser string is used?
d.Greater tension is applied?

Explain the main idea of Doppler’s effect!

If you confused, just send an email to idiredja.gunawan@gmail.com or try to meet me during the break.

Mersenne Law

2008-11-25T09:16:00.011+07:00

Mersenne is studying factors that influence frequency which will work in string and he found as follow :

Length, the longer one will decrease frequency
Diameter, the smaller one will increase frequency
Diameter could be refer to area
Tension, the bigger one will increase frequency
Density, the smaller one will increase frequency

Mathematically can be stated as

Where T = tension, L = length, A = area and p = density
If the area refer to diameter, area will be the same as d^2 (where d stands for diameter)

Work example : A man want to increase the frequency twice than previous.

What is the comparison of the length of previous and after it is increased? (Answer 2 : 1 )
What is the comparison of the diameter? (Answer 2 : 1)
What is the comparison of the density? (Answer 4 : 1)
What is the comparison of the tension? (Answer 4 : 1)

Resonance

2008-11-25T08:43:00.005+07:00

Sometimes we notice that when a source of sound vibrate, we can feel other things might vibrate altogether at the same frequency, this phenomenon is called RESONANCE.
Example, when there's a sound of plane, sometimes, we notice that the window is vibrating altogether too! This will create a louder sound at the same frequency.

Principle of resonance is also used in designing musical instrument, we can find some resonance box in a guitar that is used to make louder sound.

Basically, a resonator (mostly for a musical instrument) should have height of n/4 over the vibrating sound to vibrate altogether (creating resonance).
Example when a tuning fork vibrates at 1500 Hz (take the speed of sound in the air as 300 m/s), and you were pouring a 20 cm height of glass with water, you will hear a resonance at 5 cm height of water. Why? When a source of sound vibrate at 1500 Hz and the speed of sound is 300m/s, it means the wavelength of the sound wave created is 20 cm. To create a resonance to the glass which is filled with water, it should be n/4 over 20 cm, if n=1 it means 1/4 over 20 cm which will result 5 cm.
However if you keep on pouring the water you will hear another resonance at 10 cm (2/4 over 20 cm) and at 15 cm (3/4 over 20 cm) and the last one at 20 cm (4/4 over 20 cm).

Try below work examples :

A student is vibrating a tuning fork at 340 Hz and the speed of sound is noted as 340 m/s. This tuning fork is going to resonate to water filled measuring cylinder 1 m height. How many times will the louder sound heard when he pours water inside the cylinder? (Answer : 4 times)
How high should an air pipe to be made to create a resonance to a source of sound that vibrates at 300 Hz and the speed of sound is 300 m/s? (Answer : 25 cm)
Andy is filling a glass of water at 10 cm and try to find a resonance with a tone. If the speed of sound 300 m/s, what is the frequency of the tone should be transmitted? (750 Hz)

Sound

2008-11-24T12:26:00.011+07:00

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Everyday we talk and sing, do you know how the sound is produced.?
Sound is kind of longitudinal wave, so it means when something vibrates, the longitudinal wave is transmitted in the air that produce sound, there are some compressed air motions and rarefaction air motions.
Sound is a family of mechanical wave, so sound needs medium to transfer, without medium, there will be no sound heard.
Medium will influence how quick the sound is transmitted too!
Try to hear through a wall, water and air, you can feel the difference, the speed of sound transmitted through wall is higher than water and air, the speed of sound transmitted through water is higher than air.

Not all sound can be heard by human, only the one at our range of audibility that is 20 - 20,000 Hz. Below 20 Hz is called infrasound and above 20,000 Hz is called ultrasound.
Both kind of sound can be heard by certain animal, but not to us.

When we scream in a wide room (as a reflecting surface), some sound is reflected, this is what we call ECHO.
Echo is widely used in daily life, for example in detecting fetus (USG), SONAR, even for insect (echolocation).

When we listen to a music, we notice many notes. What create different notes is related to pitch (related to frequency), it could be higher or lower.
And so does louder sound, can be reached by increasing its amplitude.
While the same note can be sung at different waveform to create a quality (timbre), which will enrich the sound of a music.

Doppler, an Austrian scientist, notes that as one moves nearer to the source of sound, he will get the higher frequency of sound, while he moves away from the source of sound, he will get the lower frequency of sound.

2008-11-21T15:39:00.017+07:00

We are dealing with wave everyday; mobilephone, radio and internet are simple practical of radio wave. Basically, there are 2 type of wave motion that is transverse and longitudinal. Transverse wave can be found in a rope wave, ocean wave, light wave, radio wave, etc.
1 full transverse wave should consist one crest and one trough.
Longitudinal wave can be found in sound wave (when we talk or sing) and slinky wave.
1 full longitudinal wave should consist one rarefaction and one compression.
Some waves need medium to transmit, this waves are called mechanical waves, for example ocean wave need water while electromagnetic waves can be transmitted without medium, for example radio wave can work in the space.

There are many wave properties such as :
1. Frequency means number of waves in 1 second, in a radio you can know frequency by modulating its radio wave for example you can find Radio A at 92 MHz etc
2. Period means time needed for a complete wave to transmit
3. Amplitude means maximum or minimum distance that can be reach by a motion wave
4. Speed of wave means the speed of wave when it moves.
5. Wavelength means length of a full wave

From the picture below (a same motion of transverse wave, the left graph is describing its time when it moves, while the other is describing its distance when it moves), we can assume that :

a. The frequency is 0.25 Hz,
b. The period is 4 s
c. The amplitude is 6 cm
d. The speed of wave is 5 m/s
e. The wavelength is 20 m

Mathematically, we can see that the frequency is inversed to period that's why some people say that period is reciprocal to frequency.
Speed of wave can also be defined by speed of wave to travel as far as its wavelength at its period (or frequency) or speed of wave is equal to a multiplication of wavelength and frequency or wavelength divided by period.

When wave moves and finds obstacle, it will show some responses. This behavior of wave can be categorized as :
1. Reflection or bounce back of the wave when the wave hits barrier

2. Refraction or bending of wave due to different medium

3. Superposition or a coalition of two or more waves, it could be destructive wave or constructive wave
4. Diffraction or bending of wave through a slit or narrow aperture

Generally, we can divide wave into 2 parts based on their medium, mechanical wave for the wave that need medium to move and electromagnetic wave for the wave that able to move without medium. The electromagnetic wave can travel at the speed of 300.000.000 m/s in vacuum and will decrease in other medium. The electromagnetic wave is a transverse wave that has a varied wavelength, frequency and energy. The bigger the wavelength, the smallest the frequency and energy and respectively, the smaller the wavelength, the bigger the frequency and energy. The shortest wavelength in electromagnetic wave is the gamma ray and the longest one is the radio wave.

The radio wave can be used for transmitting radio and television.
The micro wave is widely used for communication and heating food.
The infra red can be used for thermal imaging and remote control.
The visible is the light that we see everyday, it has the colour of red, orange, yellow, green, blue, indigo and violet.
Ultraviolet` source mainly is sun, it can be used for sterilisation and triggering vitamin D.
X Ray is mostly used for medical in detecting bone and teeth.
Gamma is produced by radioactive reaction, it can be used for sterilisation and medical used (cancer treatment)

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Black Principle

2008-09-25T13:47:00.010+07:00

Energy can not be destroyed nor generated, but it can be transferred from one to other.
Heat is also energy, we can see that it is moving / transferring from a higher temperature to lower temperature.

2 system let say water and ice, if they are mixed together, what will happen?
Water will be colder while ice will be hotter.
They will stay at the same point (temperature), so it means heat loss from the water will be gained by ice, to make them stay balance in one temperature.

In that case we will have equation

Q loss = Q gain

What happen to solid matter when they are mixed to liquid? or solid matter when mixed to gas? and so on.

In this case, you are going to need a heating graph to see how the heat received will move point to point.

To understand the heating (cooling) graph, observe the picture below

As solid (the yellow one) receives heat, the molecule inside will vibrate faster creating space to expand and increasing the temperature. The same thing also happen to the liquid (the light blue and grey one).

During fusion / melting of solid (the green one), we will not find any temperature changes, only state (phase) changing occur, the absorbed heat will be used to overcome the intermolecular bond (which lead to state changing). This also happen during boiling / vaporizing (the blue one)

Once, you have known the step by step imminence of a substance when losing or gaining heat from the heating (cooling graph), it will be easier for you to calculate heat needed or extracted in a system which contain 2 or more state.

Ex : ice at -5C will be mixed with water at 30C, what will happen?

The ice is gaining heat while the water is losing heat, the final temperature of the two system could be below freezing point, at freezing point or above freezing point, depends on the mass of each ice or water. When the final temperature below freezing point( let say, A), it means the ice will gain heat from its heat capacity to a certain temperature (A) while water will lose heat from 30C to 0C (according to its heat capacity) and then water will change state into ice then followed by the changing temperature of the freezing water to a same number as the ice (A).

When the final temperature at freezing point ( 0C ), it means the ice will gain heat from its heat capacity to 0C then followed by the fusion of the ice into liquid while water will lose heat from 30C to 0C (according to its heat capacity).

When the final temperature above freezing point (let say, B), it means the ice will gain heat from its heat capacity to 0C, followed by fusion, turn to water then rising up its temperature to B (of course, at this poinr, it has turned to water) while water will lose heat from 30C to B.

Worked example :

Q 1 kg of alcohol (heat capacity of 3000 J/kgC) at 40C will be mixed with 1 kg of water (heat capacity of 4000 J/kgC) at 75C. What will be the final temperature of the mixture?

A Alcohol will gain heat from water. Take the final temperature as T then we can picture that the heat gained from the water will be 1 kg x 4000 J/kgC x (75-T)C. On the other hand the water will lose heat as 1 kg x 3000 J/kgC x (T-40). The number of heat gained and loss are the same, so we will get equation : 4000 (75 - T) = 3000 (T - 40) then we can find that the final temperature is 60C

Q 1 kg of ice (heat capacity of 2000 J/kgC and latent heat of fusion 300000J/kg) at -4C will be mixed with 1 kg of water (heat capacity of 4000 J/kgC) at 80C. What will the final temperature of the mixture?

A Ice will gain heat from water. Take the final temperature as 0C (stay at water) then ice will gain heat to raise temperature to 0C as 1 kg x 2000 J/kgC x ((0-(-4))C then followed by melting as 1 kg x 300000 J/kg. On the other hand the water will lose heat as 1 kg x 4000 J/kgC x (80-0). The number of heat gained and loss should be the same, however we get equation that 8000 J + 300000 J = 320000 J which is impossible because the heat loss from the water (320000 J) is over the heat gained by ice, so it means after the ice melting, it will raise temperature, let say A. It will make us to recalculate the heat gained by ice as 8000 J + 300000 J + 1 kg x 4000 J/kgC x A C and the heat loss of the water as 1 kg x 4000 J/kgC x (80-A) C. That end the equation as 308000 J + 4000A = 320000 - 4000 A which lead that the final temperature (A) is 1.5C

Q 1 kg of ice (heat capacity of 2000 J/kgC and latent heat of fusion 300000J/kg) at -4C will be mixed with 1 kg of water (heat capacity of 4000 J/kgC) at 10C. What will the final temperature of the mixture?

A Ice will gain heat from water. Take the final temperature as 0C (stay at water) then ice will gain heat to raise temperature to 0C as 1 kg x 2000 J/kgC x ((0-(-4))C then followed by melting as 1 kg x 300000 J/kg. On the other hand the water will lose heat as 1 kg x 4000 J/kgC x (10-0). The number of heat gained and loss should be the same, however we get equation that 8000 J + 300000 J = 40000 J (which is impossible), from the number we can see that heat needed for ice to become water (308000 J) is higher than the given heat from the water (40000 J) , so we can predict that not all ice become water (only port of ice, let say m) it means the equation will become 8000 J + 300000m = 40000 J, and this equation is possible. In this case the final temperature is 0C

Latent Heat

2008-09-25T13:27:00.003+07:00

Do water boil at a certain point?
Every matter will boil or melt at certain point.
When matter boil / melt at certain point, so how can heat quoted at that point?
In that case you need a term to explain heat needed when there's no temperature changes.
This will lead to LATENT HEAT.
Latent heat can be used to describe amount of heat needed to change state / phase or in the area where there's no temperature changes / constant temperature.
The amount of heat needed will be quote as :
Q = m L
where Q as quantity of heat needed to boil / melt, m as mass of the melting / boiling matter, and L as the latent heat of 1 kg of matter to boil / melt

Do you know that if you boil water in a highland, you will get point below 100C?
And so do impurities also influence boiling and melting point of water.
Study how long does it take to boil water and water with salt in it, ok :)

Heat Capacity

2008-09-25T10:28:00.006+07:00

What can you conclude from the animation?
They are having an increase in temperature when heat is given, aren't they?
The term we used to describe that matter will increase in temperature when heat is given is said HEAT CAPACITY.
At the same heat given but difference in mass, will also give a difference in temperature raise.
Now observe below animation

What can you observe from the experiment?
Both metals is increasing in temperature, however, copper will increase higher compare than aluminum, why is that?
The heat capacity of copper can be said is lower than aluminum when the same heat is given but the raise of temperature of copper is higher than aluminum.
Now, can you figure out which matter will have higher amount of heat capacity? That's right, the one with higher amount of heat capacity, mostly are isolators.

We can say that heat given will be transferred by matters to increase their former temperature.
Amount of the temperature raise depends on :

Mass of matter (from the first animation, it shows that higher mass will have lower temperature raise and so on)

Kind of matter (from the second animation, it shows that different matter has different heat capacity)

In short, we will get this equation

Water Anomalyous

2008-09-24T09:57:00.004+07:00

Observe a glass of iced water, what did you see?

Does the ice float or sink?

Ice always floats in water, isn't it?

Since ice floats in water, it means ice has lower density than water.

Lower density can be caused by:

1. Increase the volume

2. Decrease the mass

How about ice? What happen to ice to make it lower in density? Did you decrease the mass of water to be made into ice?

Of course not, generally all things will remain in mass, but change in volume (because of thermal expansion, it could expand or contract actually)

When we make ice from water, there's no changing in mass, the one which changing is state (phase, from liquid to solid).

Normally, during cooling, all matters will contract, so the volume will decrease.

However, that's not happening to water when they are changing into ice, water will expand (when we put in freezer, to make ice), that will lead to the increase of volume.

If you notice, everytime you make ice cube in a container, you will see that ice will fill the container more than you put before (when remain as water), so it is clear that ice has higher volume than water.

Since ice has higher volume than water, it means when ice melt to water, the ice will decrease in volume, to become water, normally.

But then will water remain normal? Or will it expand under hot condition and contract under cold condition?

Of course.

This will occur at 4 C and above.

That's why we say there is a strange property of water when become ice or ice when become water (anomalyous of water).

This phenomenon only occurs at 0 - 4 C.

Observe the graph below to see how volume of water interact to temperature.

You can see that at 4 C the water will reach its minimum volume, so it means the density will be the highest and then the density will increase comparable to the temperature and so on.

Heat Transfer

2008-09-23T10:28:00.008+07:00

Heat is energy, internal energy which commonly used to describe the heat of body.
Internal energy is similar to mechanical energy. So, heat can be generated as kinetics energy and potential energy. To differentiate kinetics and potential energy of heat, we can define the principle of potential and kinetics energy itself. Kinetics energy is related to the movement, for heat, the kinetics energy is described by the movement of the particle inside during heating and cooling.
Potential energy is related to the condition, thus potential energy is described by the state changing of a particle.
Energy can not be generated and destroyed, means heat can not be generated nor destroyed. It only moves from one particle to anothe.
There are several ways of heat transfer :

1. Conduction
Conduction is commonly used for all solid matter.
As one matter to other has different amount to absorb heat, we can not assume that the heat transfer for one matter to other will show the same performance.
This will lead to the understanding of conductor and isolator.
Conductor means good in heat transferring, i.e. metal.
Isolator means bad in heat transferring, i.e. wood, plastics.

2. Convection
Convection is commonly used for liquid and gas.
One characteristics of convection is the heat flow.

3. Radiation
Radiation used for gas and or vacuumed condition

Bimetallic Strips

2008-09-23T10:10:00.007+07:00

Bimetallic strips is a 2 joined metal that mesh closely to become an union.
Bimetallic strips will expand also under hot condition and contract under cold condition, however since bimetallic strips contain 2 metals, which will not expand / contract as same amount one another, they will bend according to its linear coefficient of thermal expansion.
This characteristics is very useful for electric used (mostly Mini Circuit Breaker), because they can react if there is an overheating. (Try to figure out where the bimetallic strip is).

Thermal Expansion

2008-09-22T11:28:00.014+07:00

Generally, all thing will expand under hot condition and contract / compress under cold condition.
The amount of increment during expanding or contracting for each matter will be different, based on their characteristics.
Generally, the expansion and contraction of gas is the biggest amongst other, and the expansion and contraction of liquid is bigger than solid.

To know the increment, people conducted an experiment to find the difference at certain temperature and found the number as linear coefficient of thermal expansion (for an increment in length) and volumetric coefficient of thermal expansion (for an increment in volume).

By knowing those data, you can assume which matter will give you higher length / volume under hot condition and contrary lower length / volume under cold condition.

For example if you want to create a liquid thermometer, you should find material with high expandibility for its liquid hence a low expandibility for the liquid' container (it's explained why thermometer are covered with glass, which is less to expand compare to the liquid / alcohol / mercury).

You can see also that the increment depends on the temperature changes.

What else might influence the increment?

How about the initial length or volume?

I run an experiment as follow to find their relationship.

First, I gave a matter (which has linear coefficient of thermal expansion 12 10^-6 /C and volumetric coeffiicient of thermal expansion 36 10^-6 / C) a number of temperature changes and find the increment at two point of view that is length and volume.

I got data as follow :

Second, I gave the same matters (with various length / volume) a same temperature change, then observe their final length and volume.
I got data as follow :

Can you find the relation ship of the initial, final, coefficient of thermal expansion and temperature changes?

You are right, the final length / volume will increase as the initial length / volume increase also they can be increased by getting higher temperature changes.

We can say that :

Thermometer

2008-09-22T10:18:00.007+07:00

Thermometers are widely used for measuring temperature (hot or cold one).
There are 3 kind of thermometers, that is :
1. Liquid (normally mercury or alcohol) thermometer (commonly used)
Liquid thermometer contains liquid (not solid ar gas) inside it.
This liquid could be anything as long it has characteristics as follow :

Expand at hot condition and contract at cold condition.
Good expandibility, mean amongst other liquid it will expand or contract more.
Remain as liquid at working area of the thermometer, for example if we want to create a thermometer which will be used for measuring 0 - 100C, it means we must find liquid which has melting point below 0C and has boiling point over 100C

2. Thermocouple (for higher temperature, mostly used by industry)

3. Infra Red thermometer (must be placed at certain distance to keep its accurateness)

Everyone has different sense is saying hot or cold, for example if you stay in the air conditioned room, you will say outside the room is hotter, however for the person who live in a desert, he will say the same outside room (that you say hot) is colder than his place (at the desert).
To standarized the hot or cold feeling, people create scales that is:

Celcius scale

Celcius used water for scaling, he marked the temperature when water freezes at 0C and the temperature when water boils at 100C

Reamur scale

The same principle as Celcius however the temperature when water boil at 80C

Fahreinheit scale

Fahreinheit used brine and water for scaling, the temperature when brine freezes is marked at 0F and the temperature when water boils is market at 212F

Kelvin scale

Kelvin used water' absolute zero (mean there is no action at all of the molecule at that temperature) and continue to boil at 100K

Generally we can say that the relation between Celcius scale, Reamur Scale and Fahreinhet scale can be compared as 5 : 4 : 9
And the relationship between Celcius Scale and Kelvin Scale is Celcius scale is 273 less then Kelvin scale
Why don't you try to figure their relationship by information above...
Good luck...

Can We Feel Sea Breeze in The Night?

2008-09-22T09:04:00.003+07:00

Each object has a different characteristics to absorb heat.
In this case, let say, land and water are 2 different things, each has their own ability to absorb heat.
During daytime the land is hotter than the water.
Since the hotter air (from the land) always rises up, it means the cool air (from the water) will move to replace the rising air.
It means we will feel the sea breeze during the daytime.
In the night, the water is warmer than the land, so the hot air (from the water) will rise and be replaced by the cool air from the land.
That's why land breeze occurs in the night.
If there was much heat at night, will sea breeze occur?