A long solenoid of radius 2 cm has 1000 turns/m and is surrounded by a coil of radius 10 cm having a resistance of 8 ohm. The coil is connected to a galvanometer as shown. If current of 5 A in solenoid is changed to 10 A in finite time then :
(Use $π^{2} \approx 10$ .)

Question

A long solenoid of radius 2 cm has 1000 turns/m and is surrounded by a coil of radius 10 cm having a resistance of 8 ohm. The coil is connected to a galvanometer as shown. If current of 5 A in solenoid is changed to 10 A in finite time then :

(Use $π^{2} \approx 10$ .)

TestHub · Accepted Answer

B = μ 0 ​ ni = 4 π × 1 0 − 7 × 1000 × 5 = 2 π × 1 0 − 3 T The flux is confined to the solenoid cross-section. ϕ = B π r 2 = 2 π × 1 0 − 3 × π ( 0.02 ) 2 ≈ 8 × 1 0 − 6 Wb When the current changes from 5 A to 10 A, Δ ϕ = 8 × 1 0 − 6 Wb. Q = R Δ ϕ ​ = 8 8 × 1 0 − 6 ​ = 1 0 − 6 C

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JEE Advanced 2027 (Class 12+)