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 n
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.