# Current and Voltage of electrostatic discharge

I conducted an experiment , i put a silver foil on a a CRT TV , then i open the TV, charging the foil (acting like a capacitor plate), if i approach a grounded rod to it , it will discharge with a spark of about 1.8 cm length , which is equivalent to about 18 kV. What i am really interested in is once that spark goes in the rod and becomes current, i wanted to know the voltage of that current, so i asked a question on SE and the answer that it will be 18 kV, but when i connected a LED 3V in the wire connecting the rod to the ground , it worked. Another thing, will the current be simply the charge on the plate , or a normal relation between V and R?

• Why do you think that the fact that the LED flashed means that it is not necessarily 18 kV? Mar 13, 2014 at 19:12

I cannot tell you if 18kV is correct but yes - it must be a high voltage to create such a spark. Addressing the current: It is not simply a U=RI behavior since you have a capacity in your circuit which means, that the current get less over time. This is what the circuit looks like:

Which means, that the current would behave like:

The current behaves like:

The current does not equal the charge on the plate but they are dependent on each other by the following equation:

Keep in mind that if the voltage gets too low for a spark on a certain distance the discharge process stops.

I hoped that this answer helped you and contains the information you liked to know.

• But what about voltage? If the discharge wasn't from a capacitor , in a hypothetical case, lightning , will we treat it the same way? Mar 14, 2014 at 5:17
• In this case the voltage of the discharge equals the voltage of the capacitor.If the discharge doesn't come from a capacitor you need to know how it behaves. You can e.g. generate a discharge using a high voltage source - in that case the voltage would remain mostly constant. I assume that a natural lightning behaves somehow similar to a capacitor since it actually is a capacitive effect. Mar 14, 2014 at 11:27