"Tony Hwang" wrote in message news:hpRmu.465294$,
If I measure battery output with 'scope, I don't see any slightest sign of
wave form. Not even a noise. How come? We have distinctively separate
DC and AC thpory. Ever heard of impedance in DC circuit? It is resistance
only. If that is not the cae, we have to redo all the theories.

The theories are good, you just need education on them.

One simple thing is the old teletype machines. They work by turning DC and
on off in period of around 22 miliseconds to select the leters to be
printed. The coils have an inductance of around 1 henry. While they will
pull in the levers with as little as 10 volts, it will be too slow for
correct printing. It takes so long for the DC to make its way through the
coil and the maximum magnetic field to be generated. One way around it is
to use around 150 volts and a series resistance of 2500 ohms. This keeps
the overall current down but lets the levers pull in faster.