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WAEC Physics 2012 Paper

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Question : 37

Total: 47

A 12

\Omega

resistor dissipates 8kJ of heat in 20s. Calculate the current through the resistor

5.8A
6.9A
30.0A
33.3A

Solution:

Concept:

Heat dissipated in a resistor is given by

Q=I^2Rt

.

Explanation:

Given:

Q=8\text{kJ}=8000\text{J}

,

R=12\Omega

,

t=20\text{s}

.

Substitute these values into

Q=I^2Rt

.

I^2=\dfrac{Q}{Rt}

I=\sqrt{\dfrac{8000}{12\times 20}}

I=\sqrt{\dfrac{8000}{240}}=\sqrt{33.33}

I=5.77\text{A}\approx 5.8\text{A}

.

Answer:

The current through the resistor is

5.8\text{A}

. So the correct option is A.

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