Question

In the following figure ammeter and voltmeter reads 2 amp and 120 volt respectively. Resistance of voltmeter is

• A. $100\Omega$
• B. $200\Omega$
• C. $300\Omega$
• D. $400\Omega$

Answer 1

The correct option is C $300\Omega$

Let resistance of voltmeter be $R_V$. Equivalent resistance between X and Y is $R_{XY}=\frac{75R_V}{75+R_V}$
Reading of voltmeter = potential difference across X and Y = 120 = $i\times R_{XY}=2\times \frac{75R_V}{75+R_V}\Rightarrow R_V=300\Omega$