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WAEC Physics 2014 Paper

Question : 41

Total: 48

Solution:

Concept:

Resistors in parallel combine by reciprocal addition, then add the series resistor to get total resistance. Use

V = IR

with emf

9.0\,\mathrm{V}

Explanation:

The

5\,\Omega

and

20\,\Omega

resistors are in parallel.

Their equivalent resistance is

r

\frac{1}{r} = \frac{1}{5} + \frac{1}{20} = \frac{4 + 1}{20} = \frac{5}{20}

r = \frac{20}{5} = 4\,\Omega

This

4\,\Omega

is in series with the other

5\,\Omega

resistor.

Total resistance

R = 5\,\Omega + 4\,\Omega = 9\,\Omega

Battery internal resistance is negligible, so

V = 9.0\,\mathrm{V}

Current

I = \frac{V}{R} = \frac{9}{9} = 1\,\mathrm{A}

Answer:

1.0\,\mathrm{A}

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