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The internal resistance of a cell of emf 4 V is 0.1 Ω. It is connected to a resistance of 3.9 Ω. The voltage across the cell will be ______.

Asked in GUJCET 2008 · Terminal voltage and internal resistance

• (1) 0.1 V
• (2) 3.8 V
• (3) 3.9 V
• (4) 2 V

Step-by-step solution

Why the other options are wrong

• (1) This is the voltage lost inside the cell, Ir = 1×0.1 = 0.1 V. The voltage across the terminals is what remains: 4 - 0.1 = 3.9 V.
• (2) No single slip produces 3.8 V. Sanity check: I = 4/(3.9 + 0.1) = 1 A, so only 0.1 V is lost inside the cell.
• (4) Splits the emf equally between the cell and the load. The emf divides in the ratio of the resistances, 3.9 : 0.1, not 1 : 1.

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