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JAMB Physics Past Questions & Answers - Page 95

471.

An electric generator rated 12 kW, 2 kV distribute power through a cable of resistance 20 $\Omega$ . Calculate the power loss in the cable.

120 w

360 w

720 w

2400 w

View answer & explanation

Correct answer is C

Power - IV

I = $\frac{P}{V}$

= $\frac{12000}{2000}$

I = 6A

Power loss = I $^2$ R = 6 $^2$ x 20

= 720 W

472.

An alternating current supply is connected to an electric lamp which lights with the same brightness as it does with direct current source emf 6v. The peak potential difference of the a.c supply is

4.6v

6.0v

8.5v

12.0v

View answer & explanation

Correct answer is C

V_o = V $\_{rms}$ x $\sqrt{2}$

V_o = 6 x 1.414

V_o = 8.484

= 8.5v

473.

The diagram given illustrates two charged particles W and X. The charges on W and x are respectively

negative; negative

negative; positive

positive; positive

positive; negative

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

474.

All electromagnetic waves in a vacuum have the same

wavelength

frequency

speed

amplitude

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

475.

An object is placed 20cm from a concave mirror of focal length 15cm. Calculate the linear magnification of the image formed

0.5

1.5

2.0

3.0

View answer & explanation

Correct answer is D

$\frac{1}{U} + \frac{1}{V} = \frac{1}{F}$

$\frac{1}{V} = \frac{1}{F} - \frac{1}{U}$

$\frac{1}{V} = \frac{1}{15} - \frac{1}{20}$

$\frac{1}{V} = \frac{\text{4 - 3}}{60}$

$\frac{1}{V} = \frac{1}{60}$

V = 60cm

M = $\frac{V}{U} = \frac{60}{20}$

M = 3.0cm