Question

In the circuit figure, the voltmeter reads $30V$ . The resistance of the voltmeter is

• A. $1200 \, \Omega$
• B. $700 \, \Omega$
• C. $400 \, \Omega$
• D. $300 \, \Omega$

Answer 1

Answer: (A)

The potential difference across $300 \, \Omega=60-30=30V$
Therefore the effective resistance of voltmeter resistance $R$ and $400 \, \Omega$ in parallel will be equal to $300 \, \Omega$ , as 60 V is equally divided between two parts.
So, 300 $=\frac{R \times 400}{R + 400}$
or $300R \, +120000=400R \, or \, R=1200 \, \Omega$