JEE Main · 2026 · 04 Apr 2026 · Shift 1 · Current Electricity

A voltmeter with internal resistance of

x Ω

can be used to measure upto 20 V. In order to increase its measuring range to 30 V, the required modification is to ______.

Answer: (A)

Solution

At full-scale deflection the current through the voltmeter is fixed. Initially

I = \frac{20}{x}

, and after a resistance

R

is placed in series to read

30

I = \frac{30}{x + R}

. Equating,

\frac{20}{x} = \frac{30}{x + R}

gives

20 R = 10 x

, so

R = \frac{x}{2}

, connected in series with the voltmeter.

JEE Main · 2026 · 04 Apr 2026 · Shift 1 · Single correct option