JAMB Physics Past Questions & Answers - Page 366

1,826.

Which of the following types of waves needs a medium for propagation?

sound waves

light waves

radio waves

x - rays

View answer & explanation

Correct answer is A

Sound is the only mechanical wave among the rest which are electromagnetic waves.

1,827.

Which of the following could be effectively used to reduce friction?

kerosene

grease

water

petrol

View answer & explanation

Correct answer is B

grease is more viscous than the rest of the liquids

1,828.

I. Density of the liquid.
II. Depth below the surface of the liquid.
III. Surface area of the liquid.
In which of the statement above will pressure be dependent?

I and II only.

II and III only.

I, II and III only.

I and III only.

View answer & explanation

Correct answer is A

Pressure in liquid is independent of cross sectional area of the container/ liquid
∴ the correct options are I & II

1,829.

A machine is used to lift a load of 20 N through a height of 10 m. if the efficiency of the machine is 40%, how much work is done?

80 J

500 J

300 J

120 J

View answer & explanation

Correct answer is B

Efficiency = \( \frac{\text{work output}}{\text{work input}} \times \frac{100}{1} \)

= 40 = \( \frac{20 \times 10 }{x} \times \frac{100}{1} \)
= 500J

1,830.

The instantaneous value of the induced e.m.f as a function of time is ε = ε_o sin ωt where ε_o is the peak value of the e.m.f. The instantaneous value of the e.m.f., one quarter of the period is

0.00

^ε_o/₄

^ε_o/₂

ε_o

View answer & explanation

Correct answer is D

Period is the time to complete one cycle of 360^o
=> Periodic Time T ≡ 1 cycle of 360^o
∴ ^T/₄ = ³⁶⁰/₄ = 90^o
∴ Instantaneous e.m.f E = E^o sin ωt
= E^o sin 90
But sin 90 = 1: => E = E^o x 1
= E^o