# Physics 2008 | Study Mode

Question 31
A
slip-ring
B
carbon brushes
C
split ring
D
armature
##### Explanation
To correct and A.C generator with a D.C generator the slip ring is replaced with split-ring communicator

Question 32
A
0.31 A
B
3.20 A
C
3.40 A
D
5.00 A
##### Explanation
Efficiency = (power output)/power input x 100%
= 1s VS x 100% 1p
Vp
(80)/100 = (50)/IP x 200
I P = (50 x 100)/80 x 200 = 3.125 A

Question 33
A
1.42 x 10-19J
B
3.00 x 10-19J
C
4.42 x 1010-19J
D
7.42 x 10-19J
##### Explanation
Max kinetic energy = Energy of incident electron - work function. EK = hf - w
= 6.6 x 10-34 x 6.7 x 1014 - 3 x 10-19
= 4.422 x 10-19 - 3 x 10-19
= 1.422 x 10-19J

Question 34
A
current amplification
B
power amplification
C
voltage regulation
D
energy conversion
##### Explanation
Zener diode is useful in stabilized power supply i.e to keep steady the voltage of a power supply.

Question 35
A
increases
B
decreases
C
remains the same
D
increases and then decreases
##### Explanation
Heating a pure semiconductor increases the mobility of electrons and holes and hence the conductivity. thus, the resistance decreases on heating

Question 36
A
I,II,III and IV
B
I,III, and IV only
C
I, II and III only
D
I,II and IV only
##### Explanation
Transistor is used for amplification of current, power and as a switch in logic gates.

Question 37
A
ML2T-3I-1
B
ML2T-3I-2
C
M2LT-2I-1
D
M2L2T-1I-1
##### Explanation
Electrical work W = QE,
Where Q is the quantity of change and E is the electromotive force.
E = W = FxDQ_It
Where D is the displacement,I = current and t = time
But dimension of force,
= unit of mass x unit of Acceleration
= unit of mass xunit of velocityunit of time
= unit of mass x unit of displacement__unit of time x unit of time
ML/T2 = MLT-2
Dimension of emf E
= MLT-2L = ML2T-3I-1__IT

Question 38
A
0o
B
45o
C
90o
D
180o
##### Explanation
R2 - P2 + Q2 = 122 + 52
= 144 + 25 = 169
R = 169 = 13N
angle between the forces is 90o

Question 39
A
4.0 ms-1
B
6.6 ms-1
C
12.1 ms-1
D
21.0 ms-1
##### Explanation
The force which is centripetal
F = MV2_R
=5 x 723.5
= 70
V = (Fr) and if F is tripped, then
V = (3Fr)/m
= (3x70x3.5)/5
= 12.1ms-1

Question 40
A
2.5 ms-1
B
3.0 ms-1
C
4.0 ms-1
D
4.5 ms-1
##### Explanation
Smooth plane has negligible friction
only the resultant of the perpendicular forces is acting on the body, which is given as
F =
82 + 62

=
64 + 36

=
100

= 10N
But F = Ma
a = F/M = 10/4 = 2.5 ms-1

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