Question

Question 3.1: The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4Ω, what is the maximum current that can be drawn from the battery?

Class 12 - Physics - Current Electricity Current Electricity Page-127

Answer 1

emf of car battery is 12V and internal and resistance of the battery is 0.4 ohm .
so, the maximum current will be obtained when no external resistance is offered by with joining the two terminals.
I mean, $R_{ext}=0$

see daigram,
according to Kirchoff's law,
E - r × I - Rext × I = 0 ,
here I is the maximum current passing through battery.
I = E/(Rext + r)
= 12/(0 + 0.4) = 30A

hence maximum current = 30A

Answer 2

Hey there !

Solution :

Given that,

Emf = 12 V

Internal Resistance = 0.4 Ω

Maximum current that can be drawn = ?

We know that,

Emf = Current * Internal Resistance ( Ohm's Law )

=> 12 V = I * 0.4 Ω

=> I = 12 V / 0.4 Ω

=> I = 120 V / 4 Ω

=> I = 30 A or 30 amperes.

Hence the maximum current ( I ) that can be drawn is 30 A.

Hope my answer helped :-)