Question

A voltmeter has a resistance of 100 Ω. What will be its reading when it is connected across a cell of e.m.f. 2V and internal resistance 20Ω?

Answer 1

Given: R = 100 Ω, r = 20 Ω, E = 2 V

To find: Reading of voltmeter (V)

Formula: V = E − Ir 

Calculation: Current through the circuit is given by

`I = E/(R +r) = 2/(100 + 20) = 2/120`

`I = 1/ 60 A`

From formula,

V = `2 - (1/60 xx 20)` = 2 − 0.3333

∴ V = 1.667 V

The reading on the voltmeter is 1.667 V