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Experimental Physics

JEE Main level, single correct, medium

55 of 70

Question 55 of 70

A potentiometer wire $AB$ having length $L$ and resistance $12r$ is joined to a cell $D$ of emf $\epsilon$ and internal resistance $r$ . A cell $C$ having EMF $\epsilon /2$ and internal resistance $3r$ is connected. The length $AJ$ , at which the galvanometer, as shown in the figure, shows no deflection is

Show answer and solution

Answer: (D) $\dfrac{13}{24}L$

Potential difference across

AJ=I{R}_{AJ}

=\dfrac{\epsilon }{13r}\cdot \left(\dfrac{12r}{L}\cdot x\right)

For no current in galvanometer,

\dfrac{\epsilon }{2}=

potential difference across

AJ

\dfrac{\epsilon }{2}=\dfrac{12\epsilon }{13L}x

x=\dfrac{13L}{24}

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