JEE Main · 2025 · 28 Jan 2025 · Shift 2 · Current Electricity

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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.

Answer: 2

Solution

The circuit is a Wheatstone-bridge arrangement: one arm carries 10 Ω then 20 Ω (with node A between them), the parallel arm carries R then 40 Ω (with node B between them), and a 30 Ω resistor bridges A to B, all driven by a 40 V source.

When the potential at A equals the potential at B, the bridge is balanced, so no current flows through the 30 Ω bridge resistor, and the balance condition is

\frac{10}{R} = \frac{20}{40} ⟹ R = 20 Ω

With the bridge balanced, the 30 Ω arm carries no current and can be removed from the circuit for the purpose of finding the total current. The two remaining arms,

(10 + 20) = 30 Ω

and

(R + 40) = (20 + 40) = 60 Ω

, are in parallel across the source:

R_{e q} = \frac{30 \times 60}{30 + 60} = 20 Ω

The total current drawn from the 40 V source is

I = \frac{V}{R _{e q}} = \frac{40}{20} = 2 A

JEE Main · 2025 · 28 Jan 2025 · Shift 2 · Integer answer

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JEE Main · 2025 · 28 Jan 2025 · Shift 2 · Current Electricity

Solution

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