Current Electricity Problems - Numerical 06

(a) A car has a fresh storage battery of EMF 12V, internal resistance 5.0 x 10^-² W. If the starter motor draws a current of 90 A, what is the terminal voltage of the battery when the starter is on?

(b) After a long use, the internal resistance of the storage battery increases to 500W. What maximum current can be drawn from the battery? Assume EMF of the battery to remain unchanged.

e=1.6 x 10^-¹⁹C.

Sub Topics

Suggested solution:

Suggested solution:

(a) The terminal voltage V (the voltage drop across the terminals of the battery) is related to the EMF of the battery (open circuit voltage drop) by the relation,

V = E - Ir

Now,

E = 12 V, I = 90 A

V = 12 - 4.5 = 7.5 V

(b) The maximum current from a battery can be drawn by shorting it.

Then,

V = 0

and

Clearly, the battery is useless for starting the car and must be charged again.