A storage battery of EMF 10 V and internal resistance 1 Ω is being charged by a 120 V dc supply using a series resistor of 21 Ω. What is the terminal voltage of the battery during charging?

V = 15 V

The correct answer is Option (1) → V = 15 V

EMF of the Battery, $ε_{battery}=10V$

Internal Resistance of the battery, $r=1Ω$

External voltage supply, $V_{supply}=120V$

Series Resistance ($R_{series}$) = 21Ω

$R_{total}=R_{series}+R_{battery}$

$=21Ω+1Ω=22Ω$

and,

Current (I) = $\frac{V_{supply}-ε_{battery}}{R_{total}}=\frac{120-10}{22}=5A$

$∴V_{terminal}=ε_{battery}+I×r_{battery}$

$=10+5=15V$