# Physics (2017) | Study Mode

Question 21
A
number of turns in the coil is increased
B
strength of the field magnet is increased
C
slip rings are replaced with split ring cummutator
D
coil is wound on a soft iron armature
##### Explanation
A d.c generator is one in which its current is allowed to flow in one direction even through it may vary in value an a.c generator can only be made to produce a d.c by replacing the two slip rings with a single split ring or commutator.

Question 22
A

80F

B

6.0F

C

4.0F

D

2.0F

##### Explanation
For capacitance i n parallel, 2F and 2F are in parallel,
their equivalence is 2F and 2F = 4F

The 4F generated is now in series with the remaining 4F.

The net capacitance for series connection is

$$\frac{1}{C}$$ = $$\frac{1}{4}$$ + $$\frac{1}{4}$$ = 1 + $$\frac{1}{4}$$ = $$\frac{2}{4}$$

C = $$\frac{4}{2}$$

= 2F

Question 23
A
barometer
B
thermometer
C
hygrometer
D
manometer
##### Explanation
Barometer is used to measure atmosphere pressure
Thermometer is used to measure temperature
Hygrometer is used to measure relative density of a liquid
Manometer is used to measure the pressure of a gas

Question 24
A

100w

B

200w

C

400w

D

500w

##### Explanation

Power is the time rate of doing work

i.e power = $$\frac{\text{energy}}{\text{time}}$$

Since energy = mgH

power = $$\frac{mgH}{t}$$

= $$\frac{50 \times 10 \times 5}{t}$$

= 500W

Question 25
A

2.20 $$\times$$ 10$$^3$$m

B

5.0 $$\times$$ 10$$^2$$m

C

5.0 $$\times$$ 10$$^5$$m

D

11.8 $$\times$$ 10$$^{11}$$m

##### Explanation

V = f

= $$\frac{v}{f}$$

= $$\frac{3 \times 10^8}{600 \times 10^3}$$ = 500m

= 5 $$\times$$ 102m

N.B 600KHz Frequency = 600 $$\times$$ 103Hz

Question 26
A
Tension
B
Weight
C
Impulse
D
Mass
##### Explanation
Scalar quantity is a quantity with only magnitude, it has no direction
Tension, weight, impulse are vector quantities because they have direction. Mass is the only scalar quantity there

Question 27
A
0.1 m
B
0.2 m
C
2.0 m
D
2.5 m
##### Explanation
Power of a lens = $$\frac{1}{f}$$

f = focal length

f = $$\frac{1}{p}$$

= $$\frac{1}{5}$$

= 0.2m

Question 28
A

0.04m

B

0.12m

C

0.01m

D

0.08m

##### Explanation

From Hoke's Law, F = ke, K = Constant of Force

For he first case, Force = mg,

= 0.8 $$\times$$ 10 = 8N

8 = k $$\times$$ 0.04

k = $$\frac{8}{0.04}$$

= $$\frac{200N}{m}$$

Since K is constant

For the second case, F = ke

F = 200 $$\times$$ e

e = $$\frac{F}{200}$$

= $$\frac{16}{200}$$

= 0.08m

Question 29
A
By using high resistance wire
B
By using insulated soft iron wires
C
By using low resistance wires
D
Bu using turns of wires
##### Explanation
Eddy currents are produced by the varying flux cathode, the iron core of an equipment thus reducing efficiency due to power consumption. It can be reduced by laminating the core by breaking up the path of eddy current or by increasing the resistance of the core
Usage of insulated soft iron wire is to reduce hysteresis loss
Usage of low resistance wire (thick wire) is to reduce I2R loss
Usage of thick wire is to reduce leakage heat loss due to leakage of magnetic flux
Thus the correct answer is to use high resistance wire or thin wire

Question 30
A

4.0 x 10$$^{-2}$$J

B

4.0 x 10$$^{-4}$$J

C

8.0 x 10$$^{-4}$$J

D

8.0 x 10$$^{-2}$$J

##### Explanation

c = 8F, v = 10v

Energy stored = $$\frac{1}{2}$$ cv2

= $$\frac{1}{2}$$ $$\times$$ (8 $$\times$$ 10-6) $$\times$$ 102

= 4 $$\times$$ 10$$^{-4}$$

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