The reason is that your statement is true only for sine waves. In logic circuits there is a small current spike everytime a gate switches from a logic 1 to a logic 0 and vice versa.

Hi Ian,

In my electronics schooling, we were taught that all continuous
square waves are made up odd harmonics. These "harmonics" are pure sine waves. Each non sinusodial waveform, be it a ramp, sawtooth or squarewave can be decomposed or shown to be made up of many pure sinewaves with a specific frequency order and amplitude.With such complex waveforms, I was told to use the r.m.s. value of current and voltage and then multiply them to get real power.When I turn my sig.gen on(square wave) and feed that signal into my power meter (50 Ohms load true r.m.s.), my meter says my square wave has the same power at 100Hz as it has at 100KHz,200KHz,300KHz...
I think Fourier analysis had something to do with this?

Since my schooling was free under the old grant system, and therefore perhaps worthless, can someone please clarify if my schooling was correct?

Many Regards
Darren