Find the internal resistance of a car battery with an emf of 6 V if the short-circuit current is 300 A.

Find the internal resistance of a car battery with an emf of 6 V if the short-circuit current is 300 A. what will be the direction at the battery terminals if a 0.04 ohm starter is connected to it.

In the event of a short circuit, the load resistance is zero. This means the internal resistance of the current source

Ri = U / I = 6/300 = 0.02 Ohm.

When connecting the starter to the battery, we have a series connection of the resistances Ri and the resistance of the starter Rs. Their total resistance

Ro = Ri + Rs.

Find the current when connecting the starter

Is = U / Ro = 6 / (0.04 + 0.02) = 100 A.

Then the voltage at the terminals

Uz = Is * Rs = 100 * 0.04 = 4 V.

Answer: the voltage at the terminals of the battery is 4 V.