Saturday, 28 March 2020
Tuesday, 12 March 2019
PHYSICS FORMULAS AND PRACTICE PROBLEMS
REFLECTION AT CURVED SURFACES & REFRACTION AT CURVED SURFACES:
1. Magnification : m = -v/u or m=hi/ho
2. Mirror formula, 1/f = 1/u + 1/v
3. focal length f = R/2
4. Lens formula 1/f = 1/v - 1/u
5. Lens makers fomula : 1/f = (n-1) (1/R1 - 1/R2)
6. The relation between refractive indices of media, object distance, image distance, and radius of curvature is given by :
n2/v - n1/u = (n2-n1)/R
7. In case of plane mirrors, R, F are infinity, then the power is equal to zero.
n2/v = n1/u
8. The refractive index of prism is
n = sin{[A+D]/2}/SIN [A/2]
9. Speed of wave is , v = Frequency x wavelength
10. snell's law is n1sini = n2sinr
11. A + d = i1 + i2
b>PROBLEM 3:
PROBLEMS IN PHYSICS - REFLECTION AT CURVED SURFACES
PROBLEM 1:
Where is the image formed when 8 cm tall object is placed at 20 cm. in front of a concave mirror with focal length 5 cm. Find out the size of the image also.
PROBLEM 2:
A 10 cm tall object is placed in front of a convex mirror of focal length 15 cm, Find out the image distance and write its characteristics .
b>PROBLEM 3:
10 cm focal length concave mirror is placed at 40 cm, from a wall. Calculate the object distance such that its image is formed on the wall.
PROBLEM 4:
In front of 15 cm focal length concave mirror, an object is placed at 30 cm, if the object is displaced through 10 cm towards mirror, calculate by how much distance the image is displaced?
PROBLEM 5:
The image is formed behind the mirror, at a distance of 10 cm, when an object is placed at 20 cm in front of it. Identify the type of mirror used and also calculate the focal length.
ELECTRICITY:
1. Electric current i = Q/t
2. Potential difference, V = W/Q
3. Resistance R = (Resistivity * length)/Area
4. Resistance R=V/I
5. Electric power P = V * I
6. P=V2/R
7. CONDUCTIVITY = 1/Resistivity
8. Resistors connected in series, R = R1 + R2 + R3 +.....
9. Resistors connected in parallel 1/R = 1/R1 + 1/R2 + 1/R3.......
MODEL PROBLEMS :
span style="font-family: "verdana" , sans-serif; font-size: large;">
1. If you are using an electric lamp and it lights for 6 hours and the current drawn by it is 0.24 A. Then calculate the amount of charge flowing through the lamp.
2. A circuit consists of five resistors, 10 ohm, 20 ohm, 30 ohm, 40 ohm, 50 ohm, your aim is to decrease the effective resistance using the given resistors, then how do you connect them and calculate the resultant resistance.
3. Suppose that you are using a water heater to heat the water having resistance of 90 ohm, and connected to 240 v. p.d. Determine the current flowing through the water heater.
4. Calculate the number of units when 50w, 60w, 80w electrical appliances are being used daily for 2 hours for 30 days.
br />
Wednesday, 6 February 2019
A QUICK REVISION - PHYSICAL SCIENCES
Are you ready? ...........
I : REFLECTION and REFRACTION AT CURVED SURFACES
1. Predict, Which mirror is used as rear view mirror ?
2. What is the unit of the power of the lens? Define one dioptre.
3. Suppose that a person is using a concave mirror for shaving, Where should he place his face in front of the mirror?
4. Explain the refraction of light at plane surface and curved surface? When a ray of light passes from a denser medium to rarer medium which angle is greater ? Explain.
5. Guess to get always an erect and diminished image, which mirror should be used whether convex mirror or concave mirror ? Why?
6. Suppose your friend is using a lens with power is -1D, What does it denote?
7. When you are using a spherical mirror, the magnification produced by a mirror is -2, +2, Explain the characteristics of the mirror.
8. Predict, the path of the reflected ray, when a ray of light is incident on a concave mirror along its principal axis and find the angle of reflection.
. 9.Which mirror and lens makes the paper to catch fire when focused to sunlight?
1. Give a few examples for acids and bases.
2. Write the properties of acids and bases
3. What are the indicators used to test whether a substance is acid
or a base?
4. What are the materials required to understand the reaction between acids,bases and metals?
5. Write the observations from the experiment - reaction of acids with carbonates?
6. List out the salts and their formulas
7. How many types of salts are there
8. What do you understand from the reactions between metal oxides and acids ?
9. Predict the result when non-metal oxides reacted with bases.
10. Write the importance of pH value in your daily life
11. When do you say a process is chloro-alkali process?
12. How can you say that a wet blue litmus paper is used to test the acidic property instead of a dry litmus paper?
1. What is the difference between skeltal chemical equation and balanced chemical equation?
2. Give an example for precipitation reaction and double displacement reaction.
3. Understand the following chemical equation and identify X and Y.
X + Barium Chloride -----> Y + Sodium Chloride
4. If the products in a chemical equaion are Mn and Al2O3, then predict the reactants in that equation.
5. If the reactants are Carbon dioxide and Water, then guess the products and balance the chemical equation.
6. Balance the chemical equation when Pb(NO3)2 (aq) reacted with KI (aq).
2. Define spectrum?
3. Give reason why the sky look blue?
4. Predict why the sky appear black for an astronaut?
5. Write the nature of eye lens?
6. What are the conditions to occur dispersion of light?
7. Predict the defect when a person can see only objects beyond 2m. from his eyes.
8. Suppose your friend's far point of the eye gets reduced, name his eye defect.
9. Why does ray of light splits when passed through prism?
10. Calculate the Angle of prism, whose refractive index is 1.5 and angle of minimum deviation is equal to angle of prism.
11. Draw the emergent ray, incident ray, refracted ray when a light ray passes through a prism.
10. Calculate the Angle of prism, whose refractive index is 1.5 and angle of minimum deviation is equal to angle of prism.
11. Draw the emergent ray, incident ray, refracted ray when a light ray passes through a prism.
1. Explain electromagnetic spectrum.
2. What is the relation between E, h, frequency
3. Write the units of planck's constant.
4. Explain the progress of explanation on structure of atom
5. What is the importance of Quantum numbers and write the quantum numbers for an electron which is in 4th orbit's s orbital.
6. Where and when do you apply different principles used while writing electronic configuration.
7. Write the energy levels of different orbitals in ascending order and give the reason why the electron does not enter into 3d instead of 4s
1. Define atomic mass and atomic number.
2. How the atomic mass was used earlier for scientists to classify the elements. Do all these laws valid or not?
3. Which is said to be modern law classification of elements. Explain
4. How can you identify the group and period of a given element.
5. What are the properties of atom. Explain the variations and factors affecting the properties.
6. How can you say a block is s-block, p-block, d-block, f-block?
7. Describe the metallic and non-metallic property of the elements.
8. List out the Lanthanides and actinides.
1. Write the units for electric current, charge, emf, potential difference, work done, magnetic flux, magnetic induction.
2. How electricity and magnetism are related.
3. Explain the working of a battery and when do you say a battery is able to convert chemical energy into electric energy.
4. Describe in your own words about a conductor when it is in open and closed circuit.
5. What are the differences between emf and potential difference. When emf will be potential difference? Do they equal or not?
6. Draw a circuit diagram consists of three resistors, one battery, a plug key.
7. Solve the net current using Kirchoff's laws.
8. Apply Kirchoff's voltage or loop law to find out unknown resistance or unknown current flowing through the circuit.
9. Write all the factors affecting the resistance of a conductor, write the ohm's law and how do you verify experimentally?
10. What is electromagnetic induction? How Lenz's law related to it.
11. Explain Faraday's law of electromagnetic induction.
12. Write the differences among when the current is flowing through a straight conductor, circular coil and a solenoid.
13. What are the parts present in an electric motor and dynamo.
14. Can you produce electricity from a motor?
15. Write the differences between a.c. dynamo and d.c. dynamo.
16. How oersted's experiment is helpful to understand the relation between electricity and magnetism.
Friday, 5 October 2018
EXPERIMENTS IN PHYSICS AND CHEMISTRY
;
AIM:
DEMONSTRATING CONVERGENT RAYS AND DIVERGENT RAYS
Materials required: Rubber foam piece, slipper sole, Pins
Procedure: To understand convergent rays and divergent rays from mirror, we need to take a small piece of rubber foam and draw a straight line. Put the pins along the line drawn, and appears as straight lines coming out from the foam, now bend the piece of rubber foam inwards, and then we can observe that the pins meet at a point, and now bend the rubber foam, outwards then the pins appear that they are moving away from each other.
Conclusions: Convergent rays meet to a point and divergent rays move away from each other. The experiment also help us to understand the concept of normals to the curved surfaces, in the first case, the pins act as normals to the concave mirror and in the second case, the pins move away from a point. The distance between converged or diverged point to surface is called Radius of curvature and the line is called normal.
We can observe the variation in size of the image when we move the screen towards or away from the Focus.
EXPERIMENT 5
Hold the book properly, measure the distances accurately.
Conclusion:
Least distance of distinct vision can be varied with age.
AIM: To understand dispersion of light - splitting of white light ray into seven colours
Materials required: Prism, Source of white light, [a dark room], a screen
Procedure .....The splitting of white light ray into its constituent colours is known as dispersion. To do this activity, take a prism and white light source and allow the white light to pass through the prism, then we get seven colours called VIBGYOR.
Precautions: To get a narrow beam of light, white light should be allowed to pass through a small hole of paper or wooden plank.
Observations: When white light passes through a prism, dispersion takes place and refraction can be observed.
The angle of deviation is different for different colours. Violet is deviated maximum and red is deviated least.
EXPERIMENT 7:
AIM: To prove white light is constituent of seven colors.
MATERIALS REQUIRED: Plane mirror, sunlight from sun, small tub with water
PROCEDURE:
precautions to be taken:
AIM:
DEMONSTRATING CONVERGENT RAYS AND DIVERGENT RAYS
Materials required: Rubber foam piece, slipper sole, Pins
Procedure: To understand convergent rays and divergent rays from mirror, we need to take a small piece of rubber foam and draw a straight line. Put the pins along the line drawn, and appears as straight lines coming out from the foam, now bend the piece of rubber foam inwards, and then we can observe that the pins meet at a point, and now bend the rubber foam, outwards then the pins appear that they are moving away from each other.
Conclusions: Convergent rays meet to a point and divergent rays move away from each other. The experiment also help us to understand the concept of normals to the curved surfaces, in the first case, the pins act as normals to the concave mirror and in the second case, the pins move away from a point. The distance between converged or diverged point to surface is called Radius of curvature and the line is called normal.
:
AIM: To find the focal length of a given concave mirror.
Materials required : Concave mirror, Screen, V-Stand (holder), meter scale
Procedure: Collect the required materials from your laboratory, take V-stand and place the concave mirror in V-Stand, and to find the focal length of the concave mirror, we can use sun or tree or a person at a distance can be chosen as an object. If you suppose sun as the object, then face the reflecting surface towards sun, and observe the clear image of the sun as a smallest bright spot on the screen or white paper, if you suppose tree as an object, then face the reflecting surface of the mirror towards the tree and observe an inverted image of the tree on the screen or a white paper.
The distance from the image to the pole of the mirror is known as focal length of the mirror. This distance is the distance between image and mirror as observed practically.
We can observe the variation in size of the image when we move the screen towards or away from the Focus.
Precautions: Measure the distance accurately, look at the size of the screen or white paper which should not obstruct incoming sun rays.
AIM: To find the focal length of the given convex lens
Materials required: Convex lens, V-stand, screen, candle, meter scale
Procedure:
Precautions: screen, lens should be on the same line.
Result:
Focal length can be also called as minimum limiting object distance.
AIM: To find the focal length of the given convex lens
Materials required: Convex lens, V-stand, screen, candle, meter scale
Procedure:
Collect apparatus or materials required from laboratory, place the convex lens in v-stand, and place the screen on one side of the lens, and allow the light rays coming from distant object such as a tree. Adjust the distance from the screen to the lens such that the image of the tree should be clear. The distance from the image to the optic center of the lens is called the focal length of the lens.
Result:
Focal length can be also called as minimum limiting object distance.
AIM: To understand the change in focal length of lens with surrounding medium
Materials required: Convex lens, Circular lens holder, glass tumbler, Black stone
Procedure:
Before doing the experiment, find out the focal length of the given convex lens using distant object method, and note down the value. Use the same lens and place in a lens holder. Place a black stone at the bottom in glass tumbler which is filled with water. Now slowly, place the lens holder with lens into the water, to see the clear image of the black stone. The distance from the black stone to the lens will become the focal length of the lens.
Precautions: Place the lens holder slowly into the water, the length of the tumbler should be at least 5 times than that of the focal length of the lens.
Result & Observations:
We observe that the focal length of the convex lens is increased when it is placed in water. We understand that the focal length depends on surrounding medium of the lens also.
EXPERIMENT 5
AIM: To calculate/find the Least distance of distinct vision of eye
Materials required: 30 cm scale, Any printed material(news paper, textbook), observer
Procedure:
To identify the least distance of distinct vision of eye, read a text book or news paper, at certain distance from your eye. Now you are able to read the contents from the book or paper, now you try to move the book or paper towards your eye till the contents are unable to read by you. Then you try to increase the distance from your eyes till you get clear/clarity of the letters. Ask your friend to measure the distance between your eyes and the book, this distance will be the least distance of the distinct vision of your eyes. Check the distance frequently, you can understand that whether there is any eye defect or not.
Precautions:
Hold the book properly, measure the distances accurately.
Conclusion:
Least distance of distinct vision can be varied with age.
AIM: To understand dispersion of light - splitting of white light ray into seven colours
Materials required: Prism, Source of white light, [a dark room], a screen
Procedure .....The splitting of white light ray into its constituent colours is known as dispersion. To do this activity, take a prism and white light source and allow the white light to pass through the prism, then we get seven colours called VIBGYOR.
Precautions: To get a narrow beam of light, white light should be allowed to pass through a small hole of paper or wooden plank.
Observations: When white light passes through a prism, dispersion takes place and refraction can be observed.
The angle of deviation is different for different colours. Violet is deviated maximum and red is deviated least.
EXPERIMENT 7:
AIM: To prove white light is constituent of seven colors.
MATERIALS REQUIRED: Plane mirror, sunlight from sun, small tub with water
PROCEDURE:
Take small tub and fill it with water, place the plane mirror in water such that it makes some angle with water surface and make it in the presence of sunlight, the water droplets act as prism and makes the white light into seven colors and these are reflected from the mirror and arrange the reflected light to fall on to the white wall. One can observe the formation of rainbow.
precautions to be taken:
1. arrange the demonstration under the presence of sun light.
2. the mirror should be at certain angle to the surface of water
Observations:
-white light is constituent of seven colors (VIBGYOR).
Thursday, 22 March 2018
Balancing a Chemical Equation
How to balance a chemical equation?
A chemical equation tells us the type of reaction between different reactants. Chemical equation gives the states of the reactants and products. One can calculate the amount of products required for required amount of products.
To balance a chemical equation, very interesting method is algebraic expression method.
for example: C3H8 + O2 -----> CO2 + H2O
The above reaction is to be balanced using algebraic expressions
step 1) the coefficients of Each reactants and products assumed to be a,b,c,d,...
aC3H8 + b O2 -----> c CO2 + d H2O
step 2) identify and count the number of elements on both sides of the reaction
carbon: 3a = c
hydrogen: 8a = 2d
oxygen: 2b = 2c + d
step 3) let us assume a=1, then simplify the equations for other variable values
c = 3, 2d = 8 then d = 4 if d=4 and c =3 then 2b=6 + 4 = 10, b=5
step 4) write the chemical equation using the variable values
C3H8 + 5O2 ---> 3CO2 + 4 H2O
step 5) count the number of atoms on both sides
carbon atoms = 3
hydrogen atoms = 8
oxygen atoms = 10
step 6) we conclude that the equation is said to be balanced.
Wednesday, 14 March 2018
Stephen Hawking ....
Stephen William Hawking....great Mathematician, Physicist
Prof. Stephen william Hawking was born on 8th Jan. 1942, in Oxford, England. Stephen studied at St. Albans School. Stephen was awarded Ph.D. titled "properties of Expanding Universe" in 1965. Stephen William Hawking was an English theoretical Physicist and Cosmlogist.
Important Concept from Stephen William Hawking.......
1. Hawking radiation:
This is the black body radiation which is supposed to be released by blackholes due to Quantum effects. This leads to black hole evaporation, the meaning is, Hawking radiation reduces the mass and energy of blackholes.
AWARDS :
1. The Adams Prize: The prize is named after the mathematician "John Conch Adams"
2. Eddington Medal: Royal Astronomical society awards the Eddington Medal.
3. Fundamental Physics Prize: It is awarded by Fundamental Physics Prize Foundation
TOP BOOKS WRITTEN BY STEPHEN WILLIAM HAWKING:
"A Briefer history of time" a famous book written by Stephen Hawking. A Briefer history of time books gives explanation on all the forces of physics.
Another book - "The Universe in a Nutshell".
Stephen is a fellow of the Royal society and he is a member of the US National academy of Science.
