# Physics 2010 | Study Mode

Question 31
A
low voltage
B
C
high pressure
D
low pressure
##### Explanation
pumping out of the gas in the discharge tube reduces the pressure inside the tube, therefore, electricity is conducted at low pressure

Question 32
A
5.0 x 1016 Hz
B
2.0 x 1016 Hz
C
5.0 x 1015 Hz
D
2.0 x 1015 Hz
E
No correct option
##### Explanation
E = hf
f = (E)/h = (5.44 x 10-19)/6.6 x 10-34 = 8.24 x 1014

Question 33
A
rectification of signals
B
conversion of a.c to d.c
C
amplification of signals
D
conversion of d.c to a.c
##### Explanation
transistor serve the same purpose as triode valve, which is amplification of signals.

Question 34
A
carbon
B
silicon
C
transistor
D
phosphorus
##### Explanation
A semiconductor is a material whose conductivity is between good conductor and insulator. Example of pure semi conductors are silicon and germanium

Question 35
A
has no acceleration between point F and G
B
decelerates between F and H
C
has a constant soeed between points E and F
D
Accelerates between points F and G
##### Explanation
Above are the V-t graphs for
I Uniform acceleration
II uniform retardation
III Uniform velocity
Thus the car has no acceleration between point F and G since that portion of the graph represents uniform velocity

Question 36
A
III, IV and VIII
B
II, V and VIII
C
III, VI and IX
D
I, IV and VII
##### Explanation
A bod y is said to be in stable equilibrium if after a slight displacement, the body returns to its former position. Thus, position III, VI and XI represents position of stable equilibrium

Question 37
A
0.500 J
B
0.250 J
C
0.050 J
D
0.025 J
##### Explanation

Length of the string
L = y + x = 0.5m
x = L - y
= distance moved in the direction of force (which is the weight) when the body is released But cos 60o = y/0.5
y = 0.5cos60 = 0.5 x 1/2 = 0.25
x = l - y = 0.5 - 0.25 = 0.25m
Work done = force x distance moved in the direction of force.
= 0.1 x 0.25 = 0.025J

Question 38
A
7:5
B
5:7
C
1:2
D
2:1
##### Explanation
Metals P, Q
original length lP, lQ
Increase in length lP, lQ
Linear expansivities P, Q
P/Q = 2/3 ; and lP/lQ = 3/4
But increase in length, l = l
lP = PlP
lQ = QlQ
 lP = PlP = 2 x 3 = 1 lQ QlQ 3 4 2

Ratio of increase in length of P to Q = 1:2

Question 39
A
400 ms-1
B
4,000 ms-1
C
8,000 ms-1
D
160,000 ms-1
##### Explanation
The velocity of sound in air, VT, where T is absolute temperature
Thus V = KT or K = V/T
V is independent of pressure and density at a fixed temperature.
V1/T1 = V2/T2
T1 = 16 + 273 = 289K, V1 = 340ms-1
T2 = 127 + 273 = 400K, V2 = ?
 340 = V2 289 400

 V2 = 340400 _289

= 400m/s

Question 40
A
2.52 x 10-6J
B
6.90 x 10-6J
C
2.52 x 10-4J
D
6.90 x 10-4J
##### Explanation
C = C1 + C2 + C3
= 2 + 4 + 8 = 14F
V = 6V
Energy = 1/2CV2
1/2 x 14 x 10-6 x 62
= 2.52 x 10-4 J

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