Power dissipation in inductors

[uzair_ha91]

I have found a possible mistake in my book...here's the text which contains it,


"Referring to figure, it can be seen that no power is disspated in a pure inductor. In the first quarter of cycle, both V and I are positive so the power is positive, which means that energy is supplied to the inductor. In the second quarter, V is positive but I is negative. Now power is negative which implies that the energy is returned by the inductor..."
(The figure looks "something" like this) ::
http://img25.imageshack.us/img25/485/grapha.png

Isn't V negative and I positive in the 2nd quarter according to the figure?

 

[Bob S]

The author is incorrect; I is positive and V negative in second quadrant. If the integrated area per cycle is zero, then there shouldn't be any dissipated power. Integrate sin(wt) * cos(wt) over 2 pi radians, and determine what the area is.