Electro Magnetic Induction And Alternating Currents Question 490

Question: A current of 1.5 A flows through a solenoid of length 20.0 cm, cross-section 20.0cm2 and 400 turns. The current is suddenly switched off in a short time of 1.0 millisecond. Ignoring the variation in the magnetic field the ends, the average back emf induced in the solenoid is:

Options:

A) 0.3 V

B) 9.6 V

C) 30.0 V

D) 3.0 V

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Answer:

Correct Answer: A

Solution:

  • eback=Ldidt

    where L=μ0N2Al
    eback=μ0N2Al[1.501×103]

    =4π×107(400)2×20×10420×102×(1.5×103) = 0.3 V



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