Q. In the circuit figure, the voltmeter reads 30 V. what is the resistance of the voltmeter?
A) $1200\ \Omega$
B) $700\ \Omega$
C) $400\ \Omega$
D) $300\ \Omega$
Explanation
(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 $300R\ + 120000 = 400R\ or\ R = 1200\ \Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.