A current of 10 A in a certain inductor results in a stored energy of 40 J.When the current is changed to 5 A in the opposite direction, the stored energy changes by:
A)20 J
B)30 J
C)40 J
D)50 J
E)60 J

Question

Quizplus · Accepted Answer

The change in stored energy is given by the formula ΔW = 1/2 L (I2f - I2i), where ΔW is the change in stored energy, L is the inductance, Ii and If are the initial and final currents respectively. Substituting the given values, we get:
ΔW = 1/2 L (52 - 102)
ΔW = -250/2 L
ΔW = -125 L
Since the change in current is in the opposite direction, the change in stored energy is negative. Thus, the change in stored energy is 125 L. Substituting the given values, we get:
ΔW = 125 L = 125 (40/1000) = 5 J
Therefore, the correct answer is option B, which corresponds to a change in stored energy of 30 J, not 5 J.

A Current of 10 a in a Certain Inductor Results