In an arrangement, 3n cells of emf ε and internal resistance r are connected in series. Out of 3n cells, the polarity of n cells is reversed. Current in the circuit is:
Correct answer: C. ε/3r
- A. 2ε/r
- B. 2ε/3r
- C. ε/3r
- D. ε/r
Explanation
In this arrangement, you have 3n cells, each with emf ε and internal resistance r, connected in series. When n cells have their polarity reversed, these cells effectively subtract their emf from the total emf of the circuit. So, the effective emf is (3n - n)ε = 2nε - nε = ε. The total internal resistance is the sum of the internal resistances of all 3n cells, which is 3n * r = 3r. Therefore, the current in the circuit is given by Ohm's Law as i = Eeffective / reffective = ε / 3r.Option C correctly reflects this calculation. Options A, B, and D incorrectly calculate the current by either ignoring the reversed cells or incorrectly combining the resistances and emfs.
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About Current Electricity
Steady current relates charge flow to potential difference, resistance and resistivity, including how temperature changes a conductor's resistance. Sources with internal resistance have terminal voltage below their emf when delivering current, and maximum power output occurs under a specific load condition rather than at zero resistance.
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