JEE Main 2025 Jan 28 Shift 2, Physics Q24: Wheatstone Bridge, Ammeter, Voltmeter And Potentiometer

JEE Main2025Jan 28, Shift 2Physics

The value of current $I$ in the electrical circuit as given below, when potential at $A$ is equal to the potential at $B$ , will be __________ A.

Your answer

Solution

The condition $V_{A} = V_{B}$ means no current flows through the galvanometer, i.e. the bridge is balanced. For a Wheatstone bridge balance:

$\frac{10}{R} = \frac{20}{40} \Rightarrow R = 20 Ω$ .

With the bridge balanced, the galvanometer arm is irrelevant; the two parallel branches each have resistance $10 + 20 = 30 Ω$ and $20 + 40 = 60 Ω$ .

Effective resistance $= \frac{30 \times 60}{30 + 60} = 20 Ω$ .

$I = \frac{V}{R _{eff}} = \frac{40}{20} = 2$ A.

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