When the external circuit is connected, the voltage at the poles of the source is 9 V and the current in the circuit

When the external circuit is connected, the voltage at the poles of the source is 9 V and the current in the circuit is 1,5 and what is the internal resistance of the external circuit? EMF source 15V.

Data: U (voltage at the poles of the source used) = 9 V; I (current in the circuit) = 1.5 A; ε (source EMF) = 15 V.

1) Resistance of the external circuit: R = U / I = 9 / 1.5 = 6 Ohm.

2) Let us express and calculate the internal resistance of the source used: R + r = ε / I and r = ε / I – R = 15 / 1.5 – 6 = 4 ohms.

Answer: The resistance of the source used is 4 ohms; external circuit resistance – 6 ohms.