Question

A voltmeter has a resistance of $G$ ohm and range $V$ volt. The value of resistance used in series to convert it into voltmeter of range $nV$ volt is

• A. $nG$
• B. $(n-1)G$
• C. $\frac{G}{n}$
• D. $\frac{G}{(n-1)}$

Answer 1

The correct option is B $(n-1)G$

Let $R$ be the resistance to be connected in series to convert galvanometer into voltmeter.
Hence,
$R=\frac{V}{I_g}-G$
where, $I_g$ is the current through galvanometer.
The voltmeter gives the full-scale deflection for potential difference $V$. Its resistance is $G$. Hence, $I_g=\frac{V}{G}$.
Given that $V=nV$.
Therefore,
$R=\frac{nV}{\left(\frac{V}{G}\right)}-G=(n-1)G$