WAEC Physics Past Questions & Answers - Page 150

746.

A quantity of steam at 100°C condenses to water at the same temperature by releasing 6.9 x 104J of energy. Calculate the mass of the condensed steam. [specific latent heat of vaporization of water = 2.3 x 106 J kg-1]

A.

3.0 x 10-1 kg

B.

3.0 x 10-2 kg

C.

3.0 x 10-3 kg

D.

3.0 x 10-4 kg

Correct answer is B

M = \(\frac{Q}{T} = \frac{6.9 \times 10^{4}}{2.3 \times 10^6} = 3 \times 10^{-2} kg\)

747.

The amount of energy required to change a kilogram of ice in water without a change in temperature is

A.

heat capacity of ice

B.

specific heat capacity

C.

specific latent heat of vaporisation of ice

D.

specific latent heat of fusion of ice

Correct answer is D

No explanation has been provided for this answer.

748.

How long will it take to heat 3kg of water from 28oC to 88oC in an electric kettle taking 6a from a 220V supply? [specific heat capacity of water = 4180 J kg-1K-1]

A.

120s

B.

570s

C.

600s

D.

836s

Correct answer is B

t = \(\frac{mc\theta}{IV} = \frac{3 \times 4189 \times 60}{6 \times 120} = 570s\)

749.

The silvered surface in a vacuum flask reduces heat loos due to

A.

conduction

B.

convection

C.

radiation

D.

evaporation

Correct answer is C

No explanation has been provided for this answer.

750.

The sagging of overhead electrical cables is the consequence of

A.

linear expansivity

B.

superficial expansivity

C.

cubic expansivity

D.

conductivity

Correct answer is A

No explanation has been provided for this answer.