## How was your AISSCE CBSE Class 12 Physics Exam 2013?

How was the CBSE Class 12 Physics Exam today?

Was it easy or difficult?

Many students reported that the questions were unexpected and extra ordinarily tough. What was your experience?

Were there questions beyond your comprehension?

Were there questions out of Syllabus?

Anju R  writes:

Hi,
The Physics CBSE exam was tough.It was not beyond the syllabus but it was confusing and was asked in a twisted manner.Almost all the students who prepared for the exams didnot leave any derivations,laws etc.But the saddest part was that they asked the big derivation for just one mark and only very few were asked.And most questions were unexpected ones.
It was painful when I saw that after the exam almost all the students were crying.Sitting for a whole night for studying the derivations,laws etc.. gave nothing to us other than tears.We were happy after the English exam but the Physics exam gave a terror over us about Board Exams.I think 90 %  of the students could not complete saying that it was a lengthy paper.

During the exam I could see many sitting with great confusion while few others in a hurry to complete  it and the rest of them sitting sadly.By the grace of God I completed 5 minutes before the alloted time and didn’t leave any question.I hope CBSE will consider us.

Yours sincerely,
Anju.R

## Question Bank in Physics Class XII

The collection will also be helpful for students of other syllabuses.

The file consists of syllabus, key points, collection of very short Answer (1 mark), Short answer type question – solved (2 marks), short answers (3 marks), Long answers (5 marks), Solved numericals and 3 sample papers.

The contents are arranged chapter-wise. Any student will find this a boon for easy preparation and to score better marks in Physics.

## Solutions to NCERT Physics Class 12 (Ray Optics)

1. A small candle, 2.5 cm in size is placed at 27 cm in front of a concave mirror of radius of curvature 36 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Describe the nature and size of the image. If the candle is moved closer to the mirror, how would the screen have to be moved?
Answer:Size of the candle, h= 2.5 cmImage size = h’Object distance, u= −27 cmRadius of curvature of the concave mirror, R= −36 cmFocal length of the concave mirror, f=R/2 = -18 cm

Image distance = v

The image distance can be obtained using the mirror formula:

$\frac{1}{u}+\frac{1}{v}=\frac{1}{f}$

$\frac{1}{v}=\frac{1}{f}-\frac{1}{u}$

$=\frac{1}{-18}-\frac{1}{-27}=\frac{-3+2}{54}=-\frac{1}{54}$

Therefore, v=-54cm

Therefore, the screen should be placed 54 cm away from the mirror to obtain a sharp image.

The magnification of the image is given as: $m=\frac{h'}{h}=-\frac{v}{u}$

Therefore, $h'=-\frac{v}{u}\times&space;h&space;=&space;-\frac{-54}{-27}\times&space;2.5&space;=&space;-&space;5&space;cm$

The height of the candle’s image is 5 cm. The negative sign indicates that the image is inverted and real.

If the candle is moved closer to the mirror, then the screen will have to be moved away from the mirror in order to obtain the image.

2. A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.
3. A tank is filled with water to a height of 12.5 cm. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be 9.4 cm. What is the refractive index of water? If water is replaced by a liquid of refractive index 1.63 up to the same height, by what distance would the microscope have to be moved to focus on the needle again?
4. Figures 9.34(a) and (b) show refraction of a ray in air incident at 60° with the normal to a glass-air and water-air interface, respectively. Predict the angle of refraction in glass when the angle of incidence in water is 45º with the normal to a water-glass interface [Fig. 9.34(c)].
5. A small bulb is placed at the bottom of a tank containing water to a depth of 80 cm. What is the area of the surface of water through which light from the bulb can emerge out? Refractive index of water is 1.33. (Consider the bulb to be a point source.)
6. A prism is made of glass of unknown refractive index. A parallel beam of light is incident on a face of the prism. The angle of minimum deviation is measured to be 40°. What is the refractive index of the material of the prism? The refracting angle of the prism is 60°. If the prism is placed in water (refractive index 1.33), predict the new angle of minimum deviation of a parallel beam of light.
7. Double-convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20 cm?
8. A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12 cm from P. At what point does the beam converge if the lens is (a) a convex lens of focal length 20 cm, and (b) a concave lens of focal length 16 cm?
9. An object of size 3.0 cm is placed 14 cm in front of a concave lens of focal length 21 cm. Describe the image produced by the lens. What happens if the object is moved further away from the lens?
10. What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.
11. A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15 cm. How far from the objective should an object be placed in order to obtain the final image at (a) the least distance of distinct vision (25 cm), and (b) at infinity? What is the magnifying power of the microscope in each case?
12. A person with a normal near point (25 cm) using a compound microscope with objective of focal length 8.0 mm and an eyepiece of focal length 2.5 cm can bring an object placed at 9.0 mm from the objective in sharp focus. What is the separation between the two lenses? Calculate the magnifying power of the microscope,
13. A small telescope has an objective lens of focal length 144 cm and an eyepiece of focal length 6.0 cm. What is the magnifying power of the telescope? What is the separation between the objective and the eyepiece?
14. (a)A giant refracting telescope at an observatory has an objective lens of focal length 15 m. If an eyepiece of focal length 1.0 cm is used, what is the angular magnification of the telescope?(b) If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is 3.48 × 106 m, and the radius of lunar orbit is 3.8 × 108 m.

## CBSE Physics Solved Board Question Papers 2008, 2009, 2010 & 2011 – All versions

Download CBSE Physics Solved Board Question Papers 2008, 2009, 2010 & 2011 – All versions (Delhi, Outside Delhi & Foreign)

The question Papers are in PDF format, all question papers with solution in a single file. So, it may take some time for the download to finish.

CBSE Physics Class 12 Board Question Papers 2008 to 2011 all sets (SETS I, II & III) and versions (DELHI, FOREIGN, OUTSIDE DELHI)

## Quick Revision for Class X Physics SA1

CHAPTER -12 ELECTRICITY

GIST OF THE LESSON

1. Positive and negative charges: The charge acquired by a glass rod when rubbed with silk is called positive charge and the charge acquired by an ebonite rod when rubbed with wool is called negative charge.
2. Coulomb: It is the S.I. unit of charge. One coulomb is defined as that amount of charge which repels an equal and similar charge with a force of 9 x 109 N when placed in vacuum at a distance of 1 meter from it. Charge on an electron = -1.6 x 10-19 coulomb.
3. Static and current electricities: Static electricity deals with the electric charges at rest while the current electricity deals with the electric charges in motion.
4. Conductor: A substance which allows passage of electric charges through it easily is called a ‘conductor’. A conductor offers very low resistance to the flow of current. For example copper, silver, aluminium etc.
5. Insulator: A substance that has infinitely high resistance does not allow electric current to flow through it. It is called an ‘insulator’. For example rubber, glass, plastic, ebonite etc.
6. Electric current: The flow of electric charges across a cross-section of a conductor constitutes an electric current. It is defined as the rate of flow of the electric charge through any section of a conductor.

Electric current = Charge/Time     or        I = Q/t

Electric current is a scalar quantity.

1. Ampere: It is the S.I. unit of current. If one coulomb of charge flows through any section of a conductor in one second, then current through it is said to be one ampere.                                                                                                                         1 ampere = 1 coulomb/1 second    or      1 A = 1C/1s = 1Cs-1                                                                                                                                                                                                              1 milliampere =    1 mA = 10-3 A                                                                                                                                                                                 1 microampere = 1µA = 10-6 A
2. Electric circuit: The closed path along which electric current flows is called an ‘electric circuit’.
3. Conventional current: Conventionally, the direction of motion of positive charges is taken as the direction of current. The direction of conventional current is opposite to that of the negatively charged electrons.
4. Electric field: It is the region around a charged body within which its influence can be experienced. Continue reading “Quick Revision for Class X Physics SA1”

## Sure Shot questions in Physics for CBSE Class 9 Summative Assessment (SA1)

All CBSE Schools are conducting the SA1 (First Summative Assessment) in the month of September  (Kendriya Vidyalayas have already started).  At this point, we found it would be useful to the students to have a set of sure shot questions. Practising these will essentially help you score better marks in the forthcoming exams.

## Portions for SA1

MOTION, FORCE AND WORK (Motion, Force and Newton’s Laws of motion, Gravitation)

1. Derive equations of uniformly accelerated motion using graphical representation of motion.
2. Derive F=ma
3. State the law of conservation of linear momentum. Illustrate with an example
4. State and explain Archimedes’ principle.
5. Describe an experiment to verify Archimedes’ principle.
6. Distinguish density and relative density.
7. What are the effects produced by force?
8. What is friction? How is it caused? How can it be reduced?
9. Define impulse of a force.
10. Why does a cricket fielder pulls his hands backwards while taking a catch?
11. Define inertia and explain its types with suitable examples.
12. Describe two instances each where pressure is increased by decreasing the area and pressure is decreased by increasing hte area.
13. State Newton’s universal law of gravitation
14. Define G.
15. Distinguish g and G
16. Why motion and rest are said to be relative terms?
17. Define acceleration due to gravity at a place and discuss its variation with height, depth and latitude.
18. Write the differences between mass and weight.
19. Can an object be accelerated if it is moving with constant speed? Justify your answer with an example
20. Why is a person hurt more when he falls on a concrete floor than when he falls on a heap of sand from the same height?
21. The weight of an object on the surface of moon is 1.67N and its mass on its surface is 1 kg. Calculate its weight and mass on the surface of earth, (g on earth = 10 m/s2).
22. When a horse suddenly starts running, a careless rider falls backwards. Explain why?
23. State the action and reaction in the swimming action of a swimmer.
24. A stone is thrown vertically upwards with a velocity of 40 m/s and is caught back. Taking g=10 m/s2, calculate the maximum height reached by the stone.What is the net displacement and the total distance covered by the stone?

## Summative Assessment 1 (SA1) Sample Papers for class 9 Physics

The Summative Assessment 1 is about to begin. As per request from student from various parts of India and abroad, we are publishing some solved sample papers in Physics, which we think, would help you in scoring better marks in the forthcoming SA1 exams.

(Based on Motion)

Class 9 Physics Sample Paper 1  Solved

Class 9 Physics Sample Paper 2  Solved

## Transistor as a switch – Question received via Voicemail

We received the Question “Please explain the working of a transistor as a switch” via email

http://www.electronics-tutorials.ws/transistor/tran_4.html

http://c8051.leongkj.net/learning_object/general_transistor_as_

switch.swf

## Five marks questions from Electronic Devices (Long Answer Type)

1. Explain the formation of energy Bands in solids. Distinguish between metals, insulators and semiconductors on the basis of band theory.
2. Distinguish between intrinsic and extrinsic semiconductors and the conduction in P type and N type semiconductors.
3. Explain the formation of depletion region and barrier potential in a pn junction.
4. Draw the circuit diagram used to study the Forward and reverse bias characteristics and draw the graph for forward bias and reverse bias.
5. Describe the working of a half wave rectifier  with the help of a neat labeled diagram and draw the input and output wave forms.
6. Describe the working of a full wave rectifier with the help of a neat labelled diagram and draw the input and output wave forms.
7. Draw the symbols of npn and pnp transistor. Show the biasing of a transistor and explain transistor action.
8. Describe the working of an npn transistor in CE configuration as an amplifier.
9. Explain the working of a transistor in CE configuration as oscillator.
10. Explain the action of transistor as a switch.

(Have some more idea? Post them as comments)