find the energy stored in a magnetic field .if current of 5A produces a magnetic

Question

find the energy stored in a magnetic field .if current of 5A produces a magnetic flux of 2x10^-3 wb through a coil of 500 turns?

Explanation / Answer

The energy stored in an inductor is the energy stored in its magnetic field and is given by E = 0.5*L*I^2, where L = inductance and I = current. The current in an L-R series circuit is I = If*(1 - e^-t/tc), where tc is the time constant of the circuit and If is the current at t -> ?. If = V/R. tc = L/R. Calculate tc, find I at t = 90*10^-3 sec and find E from the above formula. The voltage across the inductor is the applied voltage (12v) less the drop across the resistor. So if you have I at t = 12ms, the voltage across the inductor is 12 - I*R. (That is the easy way to get the voltage--the more direct way is to use the relation that V = L*di/dt, and compute di/dt at t = 90ms.)

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