Question

I need help with all parts

An automobile starter motor has an equivalent resistance of 0.075 Ohm and is supplied by a 12.0 V battery which has a 0.045 Ohm internal resistance. (a) What is the current to the motor in A? (b) What voltage is applied to it in V? (c) What power is supplied to the motor in kW?

Answer 1

Equivalent resistance, Rm = 0.075 Ohm.

Internal resistance, r = 0.045 ohm.

Supply voltage, V = 12 V

Part (a):

Internal resistance of battery is in series with the motor winding resistance.

So, equivalent resistance, R = Rm + r = 0.075 + 0.045 = 0.120 V

So, current in the motor = V/R = 12/0.12 = 100 A

Part (b):

Applied voltage, E = I*Rm = 100*0.075 = 7.5 V

Part (c):

Power supplied to the motor, W = I^2*Rm = 100^2*0.075 = 750 W