The EMF of the battery is equal to 2V when the current in the circuit is 2 A, the voltage at the battery

The EMF of the battery is equal to 2V when the current in the circuit is 2 A, the voltage at the battery terminals is equal to 1.8 V. find the internal resistance of the battery.

EMF = 2 V.

I = 2 A.

U = 1.8 B.

r -?

Let us write Ohm’s law for a closed circuit: I = EMF / (R + r), where I is the current in the circuit, EMF is the electromotive force of the current source, R is the external resistance in the circuit, r is the internal resistance of the battery.

(R + r) = EMF / I.

r = EMF / I – R.

Let’s write Ohm’s law for a section of the circuit: I = U / R, where U is the voltage on the external circuit.

R = U / I.

r = EMF / I – U / I.

r = 2 V / 2 A – 1.8 V / 2 A = 0.1 Ohm.

Answer: The internal resistance of the battery is r = 0.1 ohm.