What is the formula for caculating energy in a capacitor.

Expert Answers
ishpiro eNotes educator| Certified Educator

Consider the capacitor with the capacitance C, the charge on the plates q, and the potential difference between the plates U.

Then the energy stored in the capacitor is `E=(qU)/2` .

Since by definition the capacitance is `C=q/U` , the formula for energy can be rewritten in terms of C and U:

`q =CU` , so `E=((CU)U)/2=(CU^2)/2`

Alternatively, it can be written in terms of q and C:

`U = q/C` , so `E=q/2 (q/C) = q^2/(2C)`

Therefore,

`E=(qU)/2 = (CU^2)/2 = q^2/(2C)` 

 

 

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