PHYSICS VIVA QUESTIONS 2023

QUESTIONS FOR VIVA VOCE            

1. Define surface tension.

Ans. The surface of the liquid behaves like a stretched membrane

and tends to contact its surface to a minimum area. The force

acting tangentially as tension on the surface of the liquid per

unit length is known as surface tension.

2. How surface tension of water is affected by temperature of

water?

Ans. Surface tension decreases by increasing temperature.

3. What is angle of contact? How it affects the capillary rise ?

Ans. It is the angle between the tangent to the liquid surface at the

point of contact and the solid surface inside the liquid.

4. Will every liquid rise in a glass tube ?

Ans. No. If the magnitude of cohesive forces is less than adhesive

forces then the liquid level will rise in the capillary tube. If the

magnitude of cohesive force is more than adi sive forces the

level will fall down in the capillary tube.

Or

 if the angle of contact is acute there will be capillary rise

and if the angle of contact is obtuse there will be capillary de-

pression than the outer level.

5. If the diameter of the capillary tube is doubled what will hap-

pen to rise of liquid ?

Ans. The rise will be halved.

6. What are cohesive and adhesive forces? Give examples.

Ans. The force between the molecules of homogeneous substances

(same) is known as cohesive forces. The force between the

molecules of heterogeneous substances (different) is known.

as adhesive forces.

7. What is the direction of the surface tension ?

Ans. It is tangential to the surface of the liquid.

8. Give certain examples where capillary rise is involved.

Ans. The rise of oil in the wick of the lamp or candle, absorption of

ink by blotting paper, rise of water in the stem of plants etc.

SURFACE TENSION VALUES OF SOME LIQUIDS

SURFACE TENSION

Liquid  

Water

Soap Solution

Olive Oil

Glycerin

Mercury

9. What are p-type semi conductors ?

Ans. When intrinsic semi-conductors are doped with third group

elements such as Boron - Aluminium and indium etc. The semi

conductors is called p-type semi conductors.

10. What are n-type semi-conductors ?

Ans. When intrinsic semi conductors are doped with fifth group

elements such as Phosphorous, Antimony, Bismuth... etc. The

semi-conductor is called n-type semi-conductors.

11. What is p-n junction ?

Ans. A part of the silicon or germanium crystal containing p-type

impurity and another part containing n-type impurity is called

p-n junction.

12. What is depletion layer ?

Ans. It is a region on either of the junction which is free from mobile

charge carriers. The width is generally in the order of micron.

13. How the barrier potential is developed?

Ans. When depletion region is formed initially electrons from n-

region move towards p-region. n-type material becomes

positively charged and p-type material becomes negative. This

creates an electric field near the junction directed from n-region

to p-region and causes potential barrier. It stops further

diffusion of holes and electrons across the junction.

14. What are the majority and minority carriers in p-type and n-

type semi-conductors ?

Ans. In p-type the majority carriers are holes and minority carriers

are electrons in n-type majority carriers are electrons and

minority carriers are holes.

15. What is leakage current ?

Ans. When p-n junction is reverse biased few minority carriers cross

the junction and constitute a small current in reverse direction

which is called leakage current.

16. What is the principle of Meter Bridge?

Ans. The balancing condition of Wheatstone's bridge.

17. Why it is called as Meter Bridge?

Ans. The length of the wire used is exactly one meter.

18. Why small currents are used in Meter Bridge?

Ans. If large currents are passed the resistance of the wire connected

will change.

19. How can you say that the connections are correct?

Ans. When the jockey is touched the ends of the wire the

deflections in the galvanometer should be opposite.

20. Will specific resistance change with length or diameter ?

Ans. No. It is the physical property of the material but the resis-

tance will change.

21. What is the purpose of High resistance ?

Ans. To protect galvanometer from high currents. When it is short

circuited we can find exact balancing length.

22. What did you observe in length when the resistance in right

gap is increased?

Ans. The balancing length will shift towards left.

Substance

23. State Ohm's law.

Ans. Ohm's law states that the strength of the current 'I' in a con-

ductor is directly proportional to potential difference V across

its ends when physical condition and temperature remains con-

stant.

24. What is the effect of temperature in the resistance of metallic

conductor ?

Ans. When the temperature raises the resistance of metallic con-

ductor also increases.

tances. Their resistance is independent of direction of current.

The non-ohmic resistances which do not obey ohm's law are

called non-ohmic resistances. Ex: semi conductors.

25. Is Ohm's law a fundamental law involving any physical prin

ciple ?

26.Thick connecting wires are used in electrical wires. Why?

Ans. No. It only gives a definition for resistance which is applicable Ans. Resistance of thick wires is small and negligible.

in general.

27. What are ohmic and non-ohmic resistances ?

Ans. The resistances which obey ohm's law are called ohmic resis-

28. Generally with what material the resistance box is made of ?

Why?

Ans. Manganin, because its temperature co-efficient is low i.e. its

variation of resistance with temperature is less.

29. A large amount of current is not advised to be pass in the

circuit. Why?

Ans. Large currents may heat up the wires. Due to which the resis-

tance may vary.

30. How do you know whether conductor obeys Ohm's law or

not ?

Ans. If the V-I graph is a straight line graph then the conductor L

obeys ohm's law.

M

Jr. & Sr. Intermediate Physics

31. What is the principle of working of Tangent galvanometer?

Ans. The T.G works on the principle of tangent law.

32. Why the coil is arranged in magnetic meridian ?

Ans. So, that B and B

33. What is reduction factor of Tangent galvanometer?

ns. The current required to produce a deflection of 45. Since I = K

Tan 0. When 0 = 45 the I = K.

34. The reduction factor depends on what factor ?

Ans. K depends on 1) no. of turns 2) radius of the coil 3) B

35. What are the S.I. Units of B, and K?

Ans. Tesla and Ampere.

36. What is the purpose of cammutator in the circuit ?

Ans. To reverse the direction to the current, so that the direction of

magnetic field may also be reversed.

37. At what angle we get accurate results?

Ans. It is about 45 degrees. The probable accurate range is 30-60

degrees.

38. Why it is advised to keep the rheostat away from the circuit?

Ans. So that the magnetic field produced due to the current in the

wire of rheostat does not effect the T.G.

39. Which are ammeter coil and voltmeter coin in T.G. ?

Ans. 2 and 50 turn coils are known as ammeter coils and are used

for the measurement of current. 500 turn coil is called volt-

meter coil used while comparing e.m.fs using T.G.

40. Can we measure very small currents using T.G. ?

Ans. No. very small currents can not produce effective deflecting

field at the center of the coil, perpendicular to the plane.

41. If the no. of turns are increased in T.G. What happens to de-

flection ?

Ans. The deflection also increases because no. of turns increases

the strength of magnetic field produced at the center of the

coil.