Note that as the harmonic number nincreases in Eq.(4-4), the voltage
amplitude decreases. For an RLload, the impedance Zn
increases as nincreases.
The combination of decreasing Vn
and increasing Zn
makes In
decrease rapidly
for increasing harmonic number. Therefore, the dc term and only a few, if any, of
the ac terms are usually necessary to describe current in an RL load.