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.
