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WAEC Physics 2013 Paper

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Question : 19

Total: 46

An electric heater has a resistance of 50

\Omega

. When it is immersed in water and connected to mains source, it draws a current of 4.0A. Calculate the heat gained by the water if the heater is switched on for 2 minutes, assuming no heat losses to the surroundings

4200J
1600J
24000J
96000J

Solution:

Concept:

The heat gained by water equals the electrical energy converted by the heater, assuming no heat losses.

Explanation:

Use the heating formula:

H = I^2 R t

.

Given:

I = 4.0\,\mathrm{A}

,

R = 50\,\Omega

.

Convert time to seconds:

t = 2 \times 60 = 120\,\mathrm{s}

.

Substitute the values:

H = (4.0)^2 \times 50 \times 120

.

H = 16 \times 50 \times 120 = 96000\,\mathrm{J}

.

Answer:

96000\,\mathrm{J}

(Option D).

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