Question

A battery of 20 cells (each having e.m.f. 1.8 volt and internal resistance 0.1 ohm) is charged by 220 volts and the charging current is 15A. The resistance to be put in the circuit is

• A. 10.27 ohms
• B. 12.27 ohms
• C. 8.62 ohms
• D. 16.24 ohms

Answer 1

The correct option is A 10.27 ohms

The total emf of the 20 cells connected in series are $1.8\times 20=36V$.

Hence, the total voltage in the circuit is $220V-36V=184V.$
From the Ohm's law, $V=IR$. Substituting the values of Voltage and current in the equation

$R=\frac{V}{I},wegetR=\frac{184}{15}=12.27ohms$.

The internal resistance of the 20 cells is given as $20\times 0.1ohms=2ohms$.
So, the total resistance R in the circuit is $=12.27-2ohms=10.27ohms.$
Hence, the resistance in the circuit is 10.27 ohms.