Question

A voltmeter with a resistance of $50 \times 10^3 \Omega$ is used to measure voltage in a circuit. To increase its range to $3$ times, the additional resistance to be put in series is

• A. $9 \times 10^6 \Omega$
• B. $10^5 \Omega$
• C. $1.5 \times 10^5 \Omega$
• D. $9 \times 10^5 \Omega$

Answer 1

Answer: (B)

Here, $V=I_{g}R$ and $V'=I_{g}R'$ or $\frac{R'}{R}=\frac{V'}{V}$
or $R'=\frac{V'}{V}R=\frac{3V}{V}\times50\times10^{3}$
$=1.5\times10^{5}\,\Omega$
$\therefore $ additional resistance,
$=1.5 \times10^{5}-0.5\times10^{5}$
$=10^{5}\,\Omega$