A potentiometer wire of length $10 \,m$ and resistance$20 \,\Omega$ is connected in series with a $25 \,V$ battery and an external resistance $30\, \Omega$. A cell of emf $E$ in secondary circuit is balanced by $250\, cm$ long potentiometer wire. The value of $E$ (in volt) is $\frac{x}{10}$. The value of $x$ is.......
JEE MAIN 2022, Medium
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$I =\frac{25}{50}=\frac{1}{2} \,A$
$\therefore \Delta\, V =10 \,V$
$10 \,m \rightarrow 10 \,V$
$2.5\, m \rightarrow 2.5\, V$
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