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A rectangular loop of wire (3 cm × 4 cm) is placed inside a solenoid of radius 8 cm. The solenoid is 25 cm long and is wound with 1500 turns of wire carrying 4 A of current. The normal to the loop lies along the solenoid axis. If the current in the solenoid is reduced to zero in 0.2 sec., find the magnitude of the average induced emf in the loop.

(1) 0.180 mV 

(2) 36 μV 

(3) 1.8 μV 

(4) 0.25 mV 

(5) 80 μV 

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Correct option: (1) 0.180 mV


The B field strength of a solenoid is B 0 = μ in , where n = 1500 / 0.25 = 6000. The emf in the loop can then be determined from E = AμonΔi /Δt. where A = 0.03 × 0.04 = 0.0012,Δi = 4 and Δt = 0.2 Solving for the emf yields E = 0.18 mV. 

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