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

Asked in GSEB Board August 2020 · Terminal voltage and internal resistance

• (1) 0.3 A
• (2) 30 A
• (3) 3 A
• (4) 0.03 A

Step-by-step solution

Why the other options are wrong

• (1) No single slip gives 0.3 A; it would need an internal resistance of (12)/(0.3)=40 Ω. With 0.4 Ω the short-circuit current is (12)/(0.4)=30 A.
• (3) Reads the internal resistance as 4 Ω: (12)/4=3 A. The decimal point matters, (12)/(0.4)=30 A.
• (4) No single slip gives 0.03 A; it is a thousandth of the (12)/(0.4)=30 A that flows when the terminals are joined by a thick wire.

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