Question

The actual value of resistance $R$, shown in the figure is $30\Omega$. This is measured in an experiment as shown using the standard formula $R=\frac{V}{I}$, where $V$ and $I$ are the reading of the voltmeter and ammeter, respectively. If the measured value of $R$ is $5\%$ less, then the internal resistance of the voltmeter is

• A. $600\Omega$
• B. $570\Omega$
• C. $35\Omega$
• D. $350\Omega$

Answer 1

The correct option is B $570\Omega$

Using,

$\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}$

Given that measured value $5\%$ is less than internal resistance of voltmeter

$0.95R=\frac{R{R}_v}{R+R_v}$

$0.95\times 30=0.05R_v$

$\therefore R_v=19\times 30=570\Omega$