Question

When a current of 2 A flows in a battery from negative to positive terminal, the potential difference across iit is 12V. If a current of 3 A flowing in the opposite direction produces a potential difference of 15 V, the emf of the battery is

• A. 12.6 V
• B. 13.2 V
• C. 13.5 V
• D. 14.0 V

Answer 1

Answer: (B)

13.2 V

Answer 2

: Let $\varepsilon$be emf and r be internal resistance of the battery.

In first case,

$12 = \varepsilon - 2r$ …(i)

In second case,

$15 = \varepsilon + 3r$

Substract (ii) from (i), we get …(ii)

$r = \frac{3}{5}\Omega$

Putting this value of r in eqn. (i), we get

$\varepsilon = 12 + \frac{2 \times 3}{5} = \frac{60 + 6}{5} = \frac{66}{5} = 13.2V$