Friday, January 22, 2010

KVPY(PHYSICS) interview questions

1. What are the orders of drift velocity for normally applied potentials (0 to 5V) and that of random thermal
speed at room temperature say (300 K).
Ans. The drift velocity is of the order of 10m per second whereas random thermal velocity of electrons is of
the under of 105 metre per second.
2. What is the conventional direction of flow of current in a metallic conductor ?
Ans. The conventional direction of flow of current is taken as the direction of flow of positive charge from
higher potential to lower potential.
3. What is meant by ampere hour capacity of a cell ?
Ans. It is a measure of the electricity capacity of a cell, i.e., how much quantity of electricity a cell is capable
of supplying. It is measured by the product amperes x hours.
4. What do you mean by 10 A × h ?
Ans. 10 A × h means, the cell will supply 1 A current upto 10 hours. 2 A current upto 5 hours or 0.5 A current
upto 20 hours.
5. Which one is greater -e.m.f. or terminal p.d. across the cell ?
Ans. The e.m.f. is greater than the potential difference across the cell e.m.f.
6. Is it possible in any case where p.d. > e.m.f. of the cell ?
Ans. Yes, at the charging of the cell
7. Can you measure e.m.f. of a cell with a voltmeter ?
Ans. No, because it requites some current from the cell for its reading. (it is measured by potentiometer)
8. When is the Wheatstone’s bridge said to be most sensitive ?
Ans. When all the four resistances P, Q, R and S are of nearly the same order of magnitude.
9. Define figure of merit of galvanometer ?
Ans. The figure of merit which is defined as the current required to produce a deflection of one division in the
galvanometer. ( k = I/).
10. Define current sensitivity and voltage sensitivity.
Ans. Current sensitivity = /I and voltage sensitivity = /V
11. How can you measure alternating current ?
Ans. Heating effect of current, Q = I2.R.t. is independent of the direction of flow of current because I2 would
always be positive. Therefore, Hot Wire ammeter is used for this purpose.
12. Suppose you have been given two tuning forks of the same metal on which marks of the frequency
have disappeared. How will you detect the one with higher frequency ?
Ans. The one which has smaller prongs will be of higher frequency.
13. What do you mean by a note ? How does it differ from a tone ?
Ans. A tone is simple sound resulting from a pure simple harmonic motion. On the other hand a note is a
complex sound made up of a complex periodic motion as obtained by the superpositions of a number of
pure simple harmonic motions.
14. If the prongs of a fork are rubbed with a file slightly or prong of tuning fork is loaded with wax than what
will be the change in frequency in both the cases.
Ans. Frequency will decreases in both the cases.
15. If you set your watch by the sound of a distant siren, will it go fast or slow ?
Ans. go slow, [because, sound take some finite time to reach you]
16. When we start filling an empty bucket with water the pitch of the sound produced goes on changing,
why ?
Ans. Bucket used like a closed pipe
fundamental tone,  =
 
So, L decreases, then  increases and pitch is also increases
17 A tunnel is drilled across earth passing through the centre. An object is dropped in this tunnel. What will
be the time period of this object.
Ans. It will oscillate about the centre of earth, its time period will be
T = g
2 = 86.4 minute
18. If tunnel is drilled across the earth and it does not pass through the centre of earth, then what will be its
time period ?
Ans. T = g
2 = 86.4 minute
19. Time period of a simple pendulum T   . If we increase the length (l of the pendulum then what will be
the maximum time period ?
Ans. T = g
2 = 86.4 minute
20. the ball of a pendulum is hollow and filled with water. A small hole is made in the bottom of the ball, water
comes out from it. How the time period of pendulum will effect.
Ans. First it will increase then decrease.
21. If we increase the current drawn from the cell then what will be the effect on potential difference across
the cell ?
Ans. V = E– Ir, it will decrease
22. A car is moving towards north direction with speed V. What will be the induced emf in the axle of the car.
If it is moving towards east, what will be the emf induced in the axle.
Ans. (i) V is towards north
emf induced due to BH
So, e = 0 )j ˆ B j ˆv .( i ˆ   H 
emf induced due to BV
) k ˆ B ( j ˆv .[ i ˆ    V = – BV v
(ii) Car is moving towards east
so, emf due to BH
e = 0 )j ˆ B i ˆV ( j ˆ    H 
due to BV
e = )] j ˆ ( B i ˆ V [ j ˆ    V  = 0
23. What are soft and hard x-rays ? Why are they so called ?
Ans. 0.1 to 1 Å hard x-rays, 1 to 10Å soft x-rays
24. On which experiment Kepler’s laws are based ?
Ans. Tycho brahe’s experiments
25. If the earth is at one-fourth of its present distance from the sun, then what will be the duration of year ?
Ans. 1/8 the present year
Sol. T(r) 3/2 T =
1 3/ 2
 


26. Who was the first to introduce MKS system ?
Ans. Giorgi
27. A liquid boils at a temperature of which its saturated vapour pressure becomes ?
Ans. Equal to the atmospheric pressure.
28. What will be the value of C in an adiabatic change for a monatomic gas P TC ?
Ans. P1– = T–  P  TC = T  P = T(–/1–)
 P =
5 / 3

= T5/2  C = 5/2
29. What will be kinetic energy of molecules of 1g He gas at 100ºC ?
Ans. 1200 joule
30. A particle of charge +q is dropped from rest above a height ‘h’ from the surface of a uniformly charged
sphere of charge +Q and radius R. When will be the particle hit the surface of the sphere ?
Ans. Hit the surface only if h is large enough.
31. If a piece of iron is wound around by a coil and an AC current p is passed, it gets hot. Why ?
A. Hysteresis and Eddy current if the frequency is slow.
32. A mercury barometer is surrounded by a big cylinder. What happens to the level of mercury, if air is
slowly removed from the cylinder ?
A. Steadily falls.
33. A solid cylinder of diameter D is mounted on a frictionless horizontal axle. A string is wrapped around it.
A heavy mass suspended by the string strikes the ground with a velocity V. How V depends on D ?
A. V is independent of D
34. Water rises to a height of 1.25 cm in a particular capillary tube. If the tube is cut at a height of 1.0 cm.
What will happen to the level of water ?
A. Water will stay at the top
35. Optical fibres make light travel along curved lines by. How ?
Ans. using multiple total internal reflection.
36. If a prism is cut into two pieces separated at very small distance then, what will be the change in angle
of deviation ?
A. Will always remain the same
37. An observer looks at a tree of height 15m with a telescope of magnifying power 10. At what distance the
tree will appear to him ?
A. 10 times nearer
38. If radium and chlorine combine to form radium chloride the compound will be radioactive or not.
A. As radioactive as the radium content.
39. An ice cube is suspended in vacuum in a gravity free room. What will be the shape of ice cube after
some time ?
A. Ice acquire will be in spherical shape
40. What will be the dimensions of radiation pressure in case of an electromagnetic wave ?
A. Energy density
Sol. Area Displacement
Force Displacement

 =
41. What is the common name of ‘h’ used in the formula R =
 
Ans. It is called sagitta
42. What is the difference between a clock and a watch ?
Ans. Clock has a bif size its least count is 1second. Watch has smaller size its least count is 0.1s/0.25s
43. The planets whose orbits are smaller than that of the earth are called ?
Ans. Inferior planets
44. Which is lighter–moist air or dry air ?
A. moist air–(dry air + water vapour)
45. What is hoar frost ?
Ans. Change of the substance from gaseous state to solid state without changing into liquid state is known
as hoar frost.
1. How many times the speed of earth about its axis is increased so that weight of an object at equator
becomes “zero” ?
(A) 10 times (B*) 17 times (C) 27 times (D) 30 times
2. Lo is the satelliteof :
(A*) Jupiter (B) Mercury (C) Venus (D) none of these
3. Two soap bubbles of different radii are connected by a small tube. then :
(A*) Air flows from the smaller bubble to bigger bubble
(B) Air flows from the bigger bubble to smaller bubble
(C) Air will not flows in any direction
(D) None of these
33. Can a substance contract on heating ? If yes then give one example.
A. yes, ice
34. Two thermometers are constructed in the same way, except that one has a spherical bulb and the other
a cylindrical bulb. Which will respond quickly to temperature changes ?
A. Cylindrical bulb (has grater surface area).
35. Why the brake drums of a car are heated, when it moves down a hill at constant speed ?
A. Kinetic energy remains constant. but potential energy decreases and its converted into the heat energy.
36. Why a gas has two specific heats ?
A. In case of gas, volume and pressure change on heating so, specific heat of gas defined either at
constant volume or constant pressure.
38. If a door of a working refrigerator is kept open for a long time in a closed room, What will be the effect
on room temperature ?
Ans. Warm
39. Animals curl into a ball, when they feel very cold. Why ?
A. the total energy radiated by a body depends on the surface area. [low surface area produced, low
radiation of heat]
40. On which stroke the otto engine does work ?
Ans. Compression stroke
42. Define resonance.
43. How can bats see in darkness ?
Ans. Bats, produced ultrasonic waves of very small wave lengths (high frequencies) the reflected waves
from an obstacle, give the direction, nature and size of obstacle.
44. Two solid pieces one of gold and the other of silver weigh the same in water. which will weigh more in air ?
Ans. The silver piece will weigh more.


  1. is this the 11th std or 12th std interview?

  2. Those are really annoying and difficult questions. No wonder less students took physics as their major subject. Regards to the blogger for posting this.

  3. Great questions! I appreciate the collection. Do you have more questions?

  4. very much conceptual


  6. recently i have appeared for kvpy interview

    some of the question asked were

    explain the 1st and 2nd law of thermodynamics thoroughly

    why S=q[rev}/T where q is reversible

    how an engine works

    draw detailed diagram

    question related to SHM

    what will be the locus of (1-t*2/1+t*2, 2t/1+t*2)

    what will be the location when t tends to infinity

    why is be the path of planets elliptical

    what is entropy

  7. Are these SA stream questions????
    @tigerjosh: Are your questions also SA questions?