A constant current of I = 15 A exists in a solenoid whose inductance is L = 31.1

Question

A constant current of I = 15 A exists in a solenoid whose inductance is L = 31.1 H. The current is then reduced to zero in a certain amount of time. (a) If the current goes from 15 to 0 A in a time of 75 ms, what is the emf e m f induced in the solenoid? e m f = (b) How much electrical energy is stored in the solenoid? (Consider the initial energy stored.) E = (c) At what rate P must the electrical energy be removed from the solenoid when the current is reduced to 0 A in a time of 75 ms? Note that the rate at which energy is removed is the power. P =

Explanation / Answer

I = 15 A

L = 31.1 H

induced emf = - L di/dt = - 31.1* (0-15) / ( 75*10-3 ) =   

emf = 6220 Volt ...............a

b energy E = 1/2L*i2   = 0.5* 31.1 * 152   = 3498.75 J

C power = dE/dt = 3498.75 J / 75*10-3   = 46650

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