P 7.6-2 The current, i(t), in a 5-H inductor is

where the units of time are s and the units of current are A. Determine the power, p(t), absorbed by the inductor and the energy, w(t), stored in the inductor.

Hint: 2 (cos A)(sin B) = sin (A + B) + sin (A – B)

Power can be found from as usual

For an inductor

So if

Since L = 5 H, then v(t) is

Finding Power

For t ≤ 0 both i(t) and v(t) = 0, so P=0.

For t ≥ 0

Using the hint

2 (cos A)(sin B) = sin (A + B) + sin (A – B)

So Power is

Now for energy,

Since there was no current or power at t= 0, there was no energy stored at t = 0.

Alternatively one could find energy from

So which is correct? Actually using the trig identity that

So that means

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This page last updated on April 13, 2019