The following statements are given related to Wheatstone Bridge:
(A) When Wheatstone Bridge is balanced, no current flows through the galvanometer arm.
(B) Wheatstone Bridge works on the principle of Kirchhoff's law.
(C) Being a null method based experiment, the result is free from the effect of extra resistances (cell resistance) of the circuit.
(D) Wheatstone Bridge is most sensitive when all the four resistances are nearly of the same magnitude.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (B), (C) and (D)
The Wheatstone bridge has four resistances in a diamond with a galvanometer across the middle. It is analysed with Kirchhoff's rules, and it is balanced when \( P/Q = R/S \).
(A) When Wheatstone Bridge is balanced, no current flows through the galvanometer arm. — Correct. At balance the two ends of the galvanometer are at the same potential.
(B) Wheatstone Bridge works on the principle of Kirchhoff's law. — Correct. The balance condition follows from applying the loop and junction rules with zero galvanometer current.
(C) Being a null method based experiment, the result is free from the effect of extra resistances (cell resistance) of the circuit. — Correct. The balance condition contains only the four bridge resistances, not the emf or internal resistance of the cell.
(D) Wheatstone Bridge is most sensitive when all the four resistances are nearly of the same magnitude. — Correct. A small change in one arm then produces the largest relative imbalance, so the bridge is most sensitive.
NCERT (2026-27):
Wheatstone Bridge – “As an application of Kirchhoff’s rules consider the circuit shown in Fig. 3.18, which is called the Wheatstone bridge.”
Wheatstone Bridge – “… Of special interest, is the case of a balanced bridge where the resistors are such that Ig = 0. We can easily get the balance condition, such that there is no current through G.”