Question

A moving coil galvanometer has resistance 50 Ω and it indicates full deflection at 4 mA current. A voltmeter is made using this galvanometer and a 5 kΩ resistance. The maximum voltage, that can be measured using this voltmeter, will be close to:
1. 40 V
2. 15 V
3. 20 V
4. 10 V

Answer 1

Correct Answer - Option 3 : 20 V

Concept:

A voltmeter is a device used to measure the potential difference between two points in a circuit. A galvanometer can be converted into voltmeter by connecting a high resistance called multiplier in series to the galvanometer.

Calculation:

Given,

Resistance of the galvanometer G = 50 Ω

Current flowing through the galvanometer,

i_g = 4 × 10³A

Resistance of the voltmeter, R = 5 KΩ = 5000 Ω

The maximum voltage measured in the galvanometer using the voltmeter is given by,

V = i_g (G + R)

V = 4 ×10^-3 (50 + 5000)

= 4 × 10^-3 (5050)

= 20.2 V ≈ 20V

Therefore, the maximum voltage measured using the voltmeter is 20 V.