Potential energy - electrostatics

[NA19]

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I've been doing electrostatics questions and some questions use PE = 1/2 QV and other questions use PE = QV. Has anyone else encountered this? When do you use which?

 

[Romz]

I've been doing electrostatics questions and some questions use PE = 1/2 QV and other questions use PE = QV. Has anyone else encountered this? When do you use which?

If I'm dealing with capacitors I usually use 1/2QV, as it's derived from 1/2 CV^2.

However, if you're dealing with free flowing charges, as you do in electrostatics, you have to use PE = QV

Why?

Because we assume in electrostatics that Voltage = Work (J) / Q (Charge of the molecule)

is equal to

W = QV. W = Potential to do Work PE


Different story in capacitors, we integrate the Capacitance formula to get 1/2 CV^2 or 1/2 QV. Where Q is the charge of one of the plates.

Use them in their proper situations and you'll be fine