Processing math: 100%

WAEC Physics Past Questions & Answers - Page 15

71.

The period of a 10 kHz radio wave traveling at 108 ms1 is--

A.

3.0 x 105s

B.

1.0 x 104 s

C.

1.0 x 104s

D.

3.0 x 104s

Correct answer is B

The relation between period and frequency is that one is the inverse of the other.

By definition:

Frequency = 1/period.

or 

period = 1/frequency → 1/ 10,000

period = 0.0001 or 1.0 x 104 s

 

72.

Current is passed through two parallel conductors in the same direction. If the conductors are placed near each other, they will------------------

A.

move in a circle

B.

repel each other

C.

remain stationary

D.

attract each other

Correct answer is D

Two conductors with current flowing in the same direction will attract. 

73.

The reason for having a large number of turns in the coil of a moving coil galvanometer is to--------

A.

make the deflection of the needle proportional to the current

B.

increase the sensitivity of the galvanometer

C.

decrease the magnetic flux produced by the magnet

D.

make the permanent magnet stronger

Correct answer is B

Sensitivity of a galvanometer increases when number of turns, area of coil and magnetic field increase

74.

The power of the lens is +2.5D. What is the radius of the curvature?

A.

2.5 cm

B.

25.0 cm

C.

40.0 cm

D.

80.0 cm

Correct answer is D

The power of a lens is defined as the reciprocal of its focal length in metres:

P = 100f → 2.5 = 100f

where P is the power in diopters and f is the focal length in metres.

2.5 * f = 100

f = 1002.5

f = 40

Where f = r2

radius of the curvature[r] = f * 2 → 40 * 2

r = 80cm

 

75.

The periodic rise and fall in the intensity of sound produced whn two notes of nearly equal frequencies are sounded together is called?

A.

doppler effect

B.

beat

C.

interference

D.

resonance

Correct answer is B

beat, in physics, the pulsation caused by the combination of two waves of slightly different frequencies