Jolyon,If you understand how Franklin's bells work, you would understand why you need DC, not AC.
When the swinging clapper contacts the high voltage charged terminal, it conducts electrons onto its surface until it has the same charge density as the main terminal. Since like charges repel, the moving clapper is then pushed away from the fixed terminal. When it hits the grounded terminal, it loses its charge to ground, and then bounces back toward the HV terminal, and the process repeats as long as the HV is present.
If you have AC on the HV terminal, then the charge on the HV fixed terminal is varying much faster than the travel time of the moving clapper between the bells, and equally in both polarities. There would be no net force on the moving clapper, though it would vibrate back and forth a tiny bit.
I suppose that if you had a really tiny, very light clapper, and a very high applied AC voltage, you could make the system oscillate faster than the frequency of the applied AC, but I bet that you would probably just end up with an arc between the HV and ground fixed electrodes.
Dave On 4/11/2012 4:24 PM, vatercox@xxxxxxx wrote:
Why the need to rectify? Surely AC exhibits the same properties of attraction/ repulsion as DC so there should be no need and the bells should ring just as easily either way. Doesn't AC cause a deflection on a gold[leaf electroscope? Yours perplexedly, Jolyon
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