JAMB Physics Past Questions & Answers - Page 384

1,916.

A heating coil rated 1000 W is used to boil off completely 2 kg of boiling water. The time required to boil  the water is?
[Special latent heat of Vaporization of water = 2.3 x 10\(^6\) Jkg-1]

A.

1.15 x 104s

B.

1.15 x 103s

C.

4.6 x 104s

D.

4.6 x 103s

Correct answer is D

Heat supplied = Heat gained
pt = ml
T = \(\frac{ml}{p}\)

= \(\frac{2 \times 2.3 \times 10^6}{1000}\)

= 4.6 x 10\(^3\) sec

1,917.

If the pressure of the vapor on top of an enclosed liquid is equal to the atmospheric pressure, what will be the temperature of the liquid enclosed?

A.

room temperature

B.

boiling point

C.

freezing point

D.

standard temperature

Correct answer is B

Liquid boils when its saturated vapor pressure is equal to the (external) atmospheric pressure.

I.e. Boiling point at 100°c 

1,918.

An electric heater rated 220v, 1000 w is immersed into a bucket full of water, calculate the mass of water if the temperature changes from 30°c to 100°c and the current flows for 300seconds.
[specific heat capacity of water = 4200 jkg-1 K-1]

A.

4.28 kg

B.

42.86 kg

C.

1.02 kg

D.

7.14 kg

Correct answer is C

Energy supplied bythe heater = heater gained by water
pt = MCAθ
1000 x 300 = m x 4200(100 - 30)
m = (1000 x 300)/4200 x 70 = 1.02 kg

1,919.

At 4°c, the volume of a fixed mass of water is?

A.

constant

B.

minimum

C.

maximum

D.

zero

Correct answer is B

Anomalous expansion of water is at temperature ranges 0°c to 4°c u. water contract when heated from 0°c to 4°c. thus the volume of water is least at 4°c

1,920.

The thermometer whose reading is indicated by a change in color of its thermometric property is the?

A.

bi-metalic strip thermometer

B.

thermocouple

C.

platinium resistance thermometer

D.

optical pyrometer

Correct answer is D

A pyrometer is instrument for measuring high temperature.
The optical pyrometer is one in which the luminous radiation from the hot body is compared with that from a known source.