CBSE Class 12 · 2020 · Current ElectricityMultiple Choice

A potentiometer can measure the EMF of a cell because:

(A)the sensitivity of the potentiometer is large
(B)no current is drawn from the cell at balance✓ Correct
(C)no current flows in the wire of the potentiometer at balance
(D)the internal resistance of the cell is neglected

Answer: (B)

Solution

At the balance (null) point the potential drop along the potentiometer wire exactly equals the cell's EMF, so the galvanometer reads zero and \emph{no current is drawn from the cell}. The cell therefore delivers no current, there is no drop across its internal resistance, and the balancing length measures the true EMF (not the terminal voltage).

CBSE Class 12 Board · 2020 · Single correct option

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