The instrument preferred for measuring the emf of a cell more accurately is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Potentiometer
The emf of a cell is the potential difference across its terminals when no current is drawn from it. An accurate measurement must therefore take no current from the cell.
Option (1) Potentiometer — Correct. A potentiometer uses a null method: at the balance point no current flows through the cell, so the balancing length gives its emf itself.
Option (2) Meter bridge — Incorrect. A meter bridge is used to find an unknown resistance, not an emf.
Option (3) Voltmeter — Incorrect. A voltmeter draws a small current from the cell, so it reads the terminal voltage \( V = E - Ir \), which is a little less than the emf.
Option (4) Wheatstone bridge — Incorrect. A Wheatstone bridge is a circuit for comparing resistances; the meter bridge is its practical form.
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.
NCERT (Pre-rationalised edition, 2022-23):
Potentiometer – “… The potentiometer has the advantage that it draws no current from the voltage source being measured. As such it is unaffected by the internal resistance of the source.”