An automobile starter motor has an equivalent resistance of 0.0470 and is suppli

Question

An automobile starter motor has an equivalent resistance of 0.0470 and is supplied by a 12.0 V battery with a 0.0100 internal resistance.

a) What is the current (in A) to the motor?

b)What voltage (in V) is applied to it?

c)What power (in kW) is supplied to the motor?

d)Repeat these calculations for when the battery connections are corroded and add 0.0900 to the circuit. (Significant problems are caused by even small amounts of unwanted resistance in low-voltage, high-current applications.)

current (in A) ?

voltage (in V) ?

power (in kW) ?

Explanation / Answer

(A) Req = 0.0470 + 0.01 = 0.057 ohm

I = V /Req = 12 / 0.057 = 210.5 A

(b) Voltage applied to it = 12 - (210.5 x 0.01) = 9.90 volt

(c) P = I^2 R = 210.5^2 x 0.0470

= 2083.1 W

(d) I = 12 / (0.0470 + 0.010 + 0.090) = 81.63 A

V = 81.63 x 0.0470 = 3.84 Volt

P = 81.63^2 x 0.0470 Or 3.84^2 / 0.0470 = 313.2 W

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