# Physics (2017) | Study Mode

Question 11
A
A compressor
B
A refrigerator
C
Air blower
D
Air conditioner
##### Explanation
Compressor is an instrument to supply air or other gas at increased pressure
Refrigerator is an appliance to keep things cold
Air blower is used to release air
Air conditioner is used to remove heat and maintain a stable temperature in an occupied space

Question 12
A
protons
B
electrons
C
ions
D
neutrons
##### Explanation
Isotopy is due to difference in mass number, what causes the difference is the difference in the number of neutrons present

Question 13
A
Balance wheel of a watch
B
Construction of steel rail lines
C
Construction of large steel bridges
D
Fitting of tyres on wheels
##### Explanation
Thermal expansion of a solid is majorly advantageous in the use of bimetallic strip in the balance of a watch so as not to lose time

Question 14
A
kgm
B
m
C
Jm
D
m$$^{-1}$$
##### Explanation
Moment of a force is the product of a force and the perpendicular distance from the line of action of the force
Moment = force $$\times$$ distance
= N $$\times$$ m
= Nm

Question 15
A
80.00%
B
76.60%
C
66.70%
D
60.70%

Question 16
A

0.8N

B

2.5N

C

0.5N

D

1.0N

##### Explanation

Upthrust = change in weight

density = $$\frac{\text{mass}}{\text{volume}}$$

Mass of liquid displaced = Density of Liquid $$\times$$ Volume;

= 103 $$\times$$ 50 $$\times$$ 10-6m3

= 0.05kg

(Note that the volume of 50cm3 was converted to m3 by multiplying by 106) i.e 50cm3 = 50 $$\times$$ 10?6m3)

Since mass displaced = 0.05kg

Upthrust = mg = 0.05 $$\times$$ 10

= 0.5N

Question 17
A

10 cm

B

16 cm

C

5 cm

D

14 cm

##### Explanation

Magnification = $$\frac{\text{Length of camera}}{\text{distance of object from pin hole}}$$

m = $$\frac{12}{60}$$

= 0.2

Also magnification m = $$\frac{\text{Height of image}}{\text{Height of object}}$$

Height of image = m $$\times$$ height of object

= 0.2 $$\times$$ 70

= 14cm

Question 18
A

240v

B

340v

C

480v

D

57600v

##### Explanation

The relationship between the peak value and r.m.s value of electricity supply is given as

V$$_{r.m.s}$$ = $$\frac{V_o}{\sqrt{2}}$$

where Vo = peak voltage

Vo = V$$_{r.m.s}$$ x $$\sqrt{2}$$

= 240 x $$\sqrt{2}$$

= 339.5v

= 340v

Question 19
A

1

B

9

C

3

D

0.33

##### Explanation

Resistor connected in a parallel have an equivalence given by
$$\frac{1}{\text{Reff}}$$ = $$\frac{1}{3}$$ + $$\frac{1}{3}$$ + $$\frac{1}{3}$$

= $$\frac{1 + 1 + 1}{3}$$ = $$\frac{3}{3}$$ = 1

Reff = 1

Question 20
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.

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