Question

A storage battery of emf 8.0 V and internal resistance $0.5\Omega$ is being charged by a 120 V dc supply using a series resistor of $15.5\Omega$. What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?

Answer 1

$E=8V$, internal resistance $R_1=0.5\Omega$
$V=120V$, resistance $R_2=15.5\Omega$
Effective voltage $V^{{}^{\prime }}=V-E=112V$
$I=\frac{V^{{}^{\prime }}}{R_1+R_2}=7A$
Voltage across $R_1=I{R}_1=3.5V$
Terminal voltage $=8+3.5=11.5V$
Series resistor in the charging circuit limits the current drawn from the external source.