Question

A car has a fresh storage battery of emf 12V and internal resistance 0.05 ohm.The starter motor draws a current of 90 A.After long use, the internal resistance of storage battery increases to 500 ohm.What maximun current can be drawn from the battery?Assume emf of the battery to remain unchanged.

Answer 1

we know that

the relation between terminal voltage (V) and emf (E) of a battery is given as

V = E - Ir

here,

E = 12 volts

I = 90 amps

r = 0.05 ohms

so,

V = 12 - 90x0.05

thus, terminal voltage

V = 7.5 volts

now,

the maximum current will be calculated for a short circuit when voltage is zero

so, if V = 0

E = Ir

or

I_max = E/r

here,

r = 500 ohms

so,

I_max = 12/500

thus, maximum current

I_max = 0.024 amps