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WAEC Physics 2017 Paper

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Question : 42

Total: 50

A battery of e.m.f 3.0V is connected across a potentiometer wire AB of length 10

\Omega\,\text{m}^{-1}

as illustrated in the diagram above. If the jockey J makes contact at the 30cm mark, determine the resistance of length AJ and voltage across AJ.

3.0 $\Omega$ ; 0.9V
3.0 $\Omega$ ; 3.0V
3.3 $\Omega$ ; 0.3V
3.3 $\Omega$ ; 9.0V

Solution:

E = 3.0V; $\;\frac{R}{l} = 10\Omega\,\text{m}^{-1}$

l = 30cm = 0.3m; R = $10\Omega\,\text{m}^{-1} \times 0.3\,\text{m} = 3\Omega$

$\;\frac{E}{V} = \;\frac{l_1}{l_2} \Rightarrow \;\frac{3}{V} = \;\frac{1}{0.3}$

= $\;\frac{3 \times \;0.3}{1} = 0.9\,\text{V}$

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