With a potentiometer null point were obtained at $140\, cm$ and $180\, cm$ with cells of $emf$ $1.1 \,V$ and one unknown $X\, volts$. Unknown $emf$ is .............. $V$
Medium
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(d) $E = \frac{V}{l}$; $E $ is constant (volt. gradient).
$ \Rightarrow $ $\frac{{{V_1}}}{{{l_1}}} = \frac{{{V_2}}}{{{l_2}}}$
$ \Rightarrow $ $\frac{{1.1}}{{140}} = \frac{V}{{180}}$
$ \Rightarrow $ $V = \frac{{180 \times 1.1}}{{140}} = 1.41\,V$
$V = \frac{{180 \times 1.1}}{{140}} = 1.41\,V$
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