Question

I have a battery of internal resistance $20m\Omega$. When discharging with a current of 1A, the potential difference across its terminals is 2V. What is its EMF?

• A. 1.80 volts
• B. 1.98 volts
• C. 2.020 volts
• D. 2 volts

Answer 1

The correct option is C 2.020 volts

The potential difference across a battery in discharging mode is given by $V=\in$ -ir where $\in$ is the EMF of the battery and r is its internal resistance. Here, V is given to be 2V, I = 1A and
$r=20\times {10}^{-3}\Omega$
$\in =V+ir=2+1\times (20\times {10}^{-3})=2.020volts$