[quote]
other student learning difficulty and suggestion for applet ?
the other part is the area under the curve "A*sin(w*t)" to ("A*sin(w*t)")^2 is half of the rectangle form by A*A and the period T. student cannot visualize this i feel.[/quote]

That is exactly why the above applet was designed for.

Black curve $I^2(t)$ is the square of the red curve $I(t)$.
However, it is similar to Blue curve (when B=0), the only difference is there is an offset.
And the offset (difference between black curve and blue curve is a constant)
which is always half the maximum value of black curve(independent of $A$ or $\omega$).

i.e. The offset is $\frac{A^2}{2}$.