The force exerted by a magnetic field on a wire having length $L$ and current $I$ is perpendicular to the wire and given as $\left| F \right| = IL\left| B \right|$ . An experimental plot shows $(\vec F)$ as function of $L$ . The plot is a straight line with a slope $S = \left( {10 \pm 1} \right) \times {10^{ - 5}}\ AT$. The current in the wire is $\left( {15 \pm 1} \right)\ mA$ . The percentage error in $B$ is
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$\frac{d F}{d I}=I B=$ slope $(s)$

$B=\frac{S}{I}$

$\frac{\Delta B}{B}=\frac{\Delta S}{S}+\frac{\Delta I}{I}=\left(\frac{1}{10}+\frac{1}{15}\right)=\frac{1}{6}$

$\%$ Error $=\frac{1}{6} \times 100=\frac{50}{3} \%$

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