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The internal resistance of a battery of 2 V terminal voltage is 0.2 Ω. If the current flowing through the battery is 0.5 A, what will be the emf of the battery?

Asked in GSEB Board March 2020 (old course) · Terminal voltage and internal resistance

• (1) 1.99 V
• (2) 1.9 V
• (3) 2.1 V
• (4) 2.01 V

Step-by-step solution

Why the other options are wrong

• (1) No single slip gives 1.99 V. Check: the drop inside the battery is Ir=0.5×0.2=0.1 V, so the emf differs from 2 V by 0.1 V, not by 0.01 V.
• (2) Subtracts the internal drop, 2-0.1. That relation holds for a battery being charged, with current driven into it against its emf; a battery supplying current has an emf larger than its terminal voltage.
• (4) No single slip gives 2.01 V. It would need an internal drop of 0.01 V, ten times smaller than Ir=0.5×0.2=0.1 V.

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