Class 12 physics question bank

Download an excellent collection of questions with answers for CBSE Class 12 Physics

Question Bank in Physics Class XII

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

Central Board of Secondary Education

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.

Relatively relative

Most of you might know einstein as being synonymous with genius. Yes he is the epitome of creative science and is still regarded as idols by some of the finest scientists of the world. Even the top most scientists considered him as being a revolutionary as his out of the box thinking. Today we are going to touch upon his theory of special relativity.

Right so first we shall discuss a bit about relative speeds.
Let us suppose that there be a system of two bodies named a and b respectively which were moving with velocities va and vb respectively towards the left. Now if you were standing on the ground at rest you would notice that both moved towards the left with velocity va and vb respectively. However if you were on the object a you would notice that the velocity of b looks to you like va-vb towards you(towards a) (here we are considering that va>vb)however if you were on b you would notice that b is moving towards you with velocity vb-va. Now if one of the objects were to be accelerated and supposing you were on the accelerating body you would feel as if a pseudo force was acting upon you which caused you (the object ) to move towards the other object with a greater speed. Hence to find out the real force acting upon you you would need to have an observer in the inertial frame of reference. However where is this frame of reference?
If you think about it you yourself are not in an inertial frame of reference  are you?
You are rotating on the earth and a rotating body is certainly not an inertial frame of reference as there is a pseudo force acting here as well called the centrifugal force.
So is there any point in the universe which can be called an inertial frame of reference? Scientists began looking for this stationary frame of reference and they were fixed upon ether. Ether was supposed to be a hypothetical jelly like fluid medium through which light propagates. However the michelson-morley experiment disproved the existence of ether. Hence scientists were now worried as without any fixed frame of reference they could not work out the electromagnetic theory as proposed by Maxwell for maxwell’s theory of electromagnetic waves were absolutely perfect in their description.
Now this is where einstein comes into the picture. He had been continuously thinking of how to make the electromagnetic theory work without the need of an inertial frame of reference. And then while looking at a big clock tower he finally found his eureka moment. He had been thinking if the speed of light was the same in all inertial frames and didn’t know how to make that work. That’s when it hit him that maybe time was affected in the overall process. And then he postulated his special theory of relativity.
The two postulates of his special theory of relativity are:
1) the laws of physics are the same in all inertial frames of reference.
2) the speed of light is constant in all frames of reference.
These two postulates worked perfectly as it has been measured to be found that the speed of light was truly constant in all inertial frames of reference.
Here is what this means. In our previous example we used the objects a and b. Now let us suppose that a shone a torch light towards b. Let the speed of light to an inertial frame of reference be c. Then the light beam is supposed to have reached b at a speed of c-(va-vb).
However it will be found that the speed with which the light beam still reached b is still c.
It discarded the need of an absolute inertial frame of reference and hence the notion of ether.

However it had certain consequences as well like time dilation and space contraction!
What are they?
Well here is a brief example of what it might look like.
Supposing there was an observer in the S frame which is relatively at rest to another frame and suppose there was another frame S’ which moved with a velocity v with reference to the stationary frame S.
Velocities (and speeds) do not simply add. If the observer in S measures an object moving along the x axis at velocity u, then the observer in the S′ system, a frame of reference moving at velocity v in the x direction with respect to S, will measure the object moving with velocity u’ where (from the Lorentz transformations above):
The other frame S will measure:
Notice that if the object were moving at the speed of light in the S system (i.e. u = c), then it would also be moving at the speed of light in the S′ system. Also, if both u and v are small with respect to the speed of light, we will recover the intuitive Galilean transformation of velocities

phew!!!

While the equations do look big and scary i will try to make it look fascinating instead. If you look at the equations a bit more carefully you will see that at speeds close to the speed of light.
From these equations you will find that even the speeds of both the frame and the object cannot exceed the speed of light.
C+C is not equal to 2C!!

Also here are some more scary equations…Bear with me!
Consider two observers O and O’ , each using their own Cartesian coordinate system to measure space and time intervals. O uses (t, x, y, z) and O ‘ uses (t’ , x’ , y’ , z’ ). Assume further that the coordinate systems are oriented so that, in 3 dimensions, the x-axis and the x’ -axis are collinear, the y-axis is parallel to the y’ -axis, and the z-axis parallel to the z’ -axis. The relative velocity between the two observers is v along the common x-axis. Also assume that the origins of both coordinate systems are the same, that is, coincident times and positions. Then?
where:

  • v is the relative velocity between frames in the x-direction,
  • c is the speed of light, is the Lorentz factor,  again for the x-direction.

 

Here is what these equations tell you. They tell you that if you were moving towards an object which is stationary with reference to a stationary frame of reference with a speed close to that of the speed of light, the moving object would find  takes greater time  to travel a certain distance than if it were measured by an observer on the fixed reference frame. Meaning?
Time slowed down for the fast moving object.
Also in the frame of reference of the moving object itself. It would find that the moving object had to travel a lesser distance than what it would have to travel as measured from the frame of reference of the stationary observer.

I have not explained the works to my readers as it would go on for pages. However I hope you understood how relativity opens up the doors to slowing down time or contracting space! Einstein wasn’t a genius for nothing! He literally opened up the door for turning something as fictional as star wars into a living reality!!

Black holes-Not exactly Black!!

Black holes-Not exactly Black!!
Now we have known black holes as giant swirling  holes present in the universe which are known to swallow anything that comes close to it. Yes we have had countless rumors and fantasies about black holes being warps in time , a portal to another dimension and the doorway to a mirror world. Of course black holes don’t really do something like that but that doesn’t mean they are not fascinating by themselves.
The mystery of black holes has fascinated physicists, scientists and certainly many others alike with their mysterious behavior. Their birth, evolution etc. are still under study and are  the objects of obsession of most astrophysicists.
clip_image002
So If it’s not a portal to the next dimension then what is it and where do the objects that it pulls inwards disappear to?
Well think of it this way. You may have heard of how  when a body of mass m and another mass M attract each other with a force given by
                                                          F=G.M.m
                                                                 r2
And the fact because of this force the potential energy that exists between them is
                                                      P.E. = G.M.m 
                                                                       r
And also the fact that escape velocity can be found by equating it with kinetic energy of the object to be equal to it’s potential energy
                                                   K.E.= 0.5 m.v2  
Now equating the kinetic energy with the potential energy we get
                                                 v2 =G. m
                                                           r
Now imagine a mass with gigantic (and i really mean it)  mass and really tiny radius        
such that                                G.M      =c2
                                                r
where c is the speed of light.
clip_image004
Yes that’s what black holes exactly are. They are objects having mass and sometimes having charge as well as angular momentum such that any object on it will have to travel at the speed of light just to escape.  So that explains why all objects cannot escape the gravitational pull of a black hole. 
Is it that strong?
Well it is so strong that it is known to even absorb light. That’s right! Black holes actually bend gravitational space around it so much that even light cannot escape it’s pulling power. Scientists have named this as the infinite space time curvature!! At this point the state of the system is called singularity. In the state of singularity the some of Einstein’s equations along with some other big equations give weird solutions the details of which i will not bore you with. But what i will say is that any mass near this point of singularity  will have time running down slower for it!(Time travel theories anyone?!!)
Why are scientists so obsessed with it?
Well for one thing they hold vital clues as to the origin of the universe. It’s true. The requirement of the formation of black holes is gigantic mass and small radius. That was the condition of the universe just a few moments before and after the big bang. So when that small point exploded in the event of the big bang many black holes were formed as the universe was expanding. So the black holes we study including the one at the centre of our galaxy is a by product of the big bang. So we can actually figure out where it all began!
So how are they formed?
Well like i told you the big mass and small radius is a good condition for the formation of black holes. So lots of black holes were formed after the big bang. Also lots of black holes are formed when massive stars collapse due to their own gravitational pull.  But of course once formed it doesn’t stay together forever. It slowly decays by means of a radiation called Hawking’s radiation.
So where do these masses disappear into?
Well that is something no one is sure of! Yes that’s true. Nobody really knows what happens to all that sucked up mass. While it is true that a lot of the mass is emitted as energy from the accretion disks.  In fact accretion disks are some of the brightest stuff in the universe. Not so black any more right?
clip_image006But scientists have found that this energy emitted as energy does not equal the energy obtained from the mass energy equivalence (any one remember Einstein’s epoch changing equation? e=mc2) energy obtained from the mass swallowed. (Though it is more efficient than fusion or fission as they use of 0.4% of the mass to be converted to energy while accretion disk formation uses 40% of the relative rest mass!)In fact information is lost inside the black hole. It would have been ok if black holes existed forever but the fact is they don’t. They decay through hawking’s radiation and hence it seems that the information is truly lost. In quantum mechanics this is the same as violation of conservation of energy!
So next time your physics teacher tells you that nothing violates the conservation of energy you might wanna raise your hand and ask him/her about black holes. If he is genuinely interested in learning he will certainly try to help you explain better.

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)

Central Board of Secondary Education

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)

Click Here to Download. 

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)

Long Answer Type Questions

  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?
  25. Read more at: http://www.icbse.com/papers/cbse-sample-paper-2011-science-class-ix

    Read more at: http://www.icbse.com/papers/cbse-sample-paper-2011-science-class-ix

 

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.

india calcutta bookstore

(Based on Motion)

 

Class 9 Physics Sample Paper 1  Solved

Class 9 Physics Sample Paper 2  Solved

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