Question

Resistor R1=3.0 Ohm is connected in series to a parallel combination of R2=9.0 Ohm and R3=7.0 Ohm. The combination of three resistors is connected to a real battery of emf 12.0 V. Find internal resistance of a battery if current through a battery is 0.40 A. Give answer in Ohms.

Answer 1

As given that a 3 ohms resistance is connected in series with the parallel combination of 9 ohms and 7 ohms

So the parallel equivalent resistance of 9 and 7 ohms resistance will be

Now this resistance ia in series with 3 Ohms resistance

So equivalent resistance of the circuit will be

Now applying kirchoff's law to the condition above the

Where V is the emf of the battery and I is the current flowing through the circuit and Rc and r are the resistance of the circuit and internal resistance respectively

By substituting the values