The meter bridge is a device

The correct answer is Option (3) → to measure resistance

A meter bridge is a practical form of the Wheatstone bridge: a one-metre wire with a jockey, and a known and an unknown resistance in the two gaps. The bridge is balanced when

    \( \displaystyle \frac{R}{S} = \frac{l}{100 - l} \)

so an unknown resistance \( S \) can be found from the balance length \( l \).

Why the other options are incorrect

• Option (1) to compare potential differences — Incorrect. Comparing potential differences is a use of the potentiometer, not of the meter bridge.

• Option (2) to measure potential difference — Incorrect. Measuring a potential difference is also a use of the potentiometer.

• Option (4) to compare emfs of two sources — Incorrect. Comparing the emfs of two cells is a use of the potentiometer.

NCERT (2026-27):
Wheatstone Bridge – “… The Wheatstone bridge and its balance condition provide a practical method for determination of an unknown resistance.”

Wheatstone Bridge – “… A practical device using this principle is called the meter bridge.”