JAMB Physics Past Questions & Answers - Page 427

2,131.

A 2000W electric heater is used to heat a metal object of mass 5kg initially at 10oC. If a temperature rise of 30oC is obtained after 10min, the heat capacity of the material is

6.0 x 10⁴J^oC^-1

4.0 x 10⁴J^oC^-1

1.2 x 10⁴J^oC^-1

8.0 x 10⁴J^oC^-1

View answer & explanation

Correct answer is A

2000W heater → 2000J/S
=> Heat supplied by the heater within 10 min
(600 seconds) = 2000 x 600
= 1200000J
∴ Heat capacity MC = 1200000/(30-10)
= 60000J/C
Heat capacity = 6.0 x 104J/C

2,132.

If the distance from a point source of sound is doubled, by what factor does the intensity decrease?

4.00

2.00

0.50

0.25

View answer & explanation

Correct answer is A

In general intensity of a wave is the rate of flow of energy across unit area normal to the direction of propagation of the wave intensity α1/r2 where r is the distance away from the point source. Thus if the distance from the point source of the sound wave is doubled, then the intensity will be decreased by a factor of 4

2,133.

At what position will an object be placed in front of a concave mirror in order to obtain an image at infinity?

At the pole of the mirror

At the principal focus

at the center of the curvature

Between the principal focus and the center of curvature

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

2,134.

The phenomenon where by the water droplets in the atmosphere combines with dust particles in the air to reduce visibility is

cloud