Calculating energy stored in a capacitor
- Recall that the electric potential energy is equal to the area under a potential-charge graph
- This is equal to the work done in charging the capacitor across a particular potential difference
- Therefore the work done, or energy stored in a capacitor is defined by the equation:
- If the charge Q is substituted using the capacitance equation, Q = CV, the work done can also be defined as:
- Where:
- W = work done/energy stored (J)
- Q = charge on the capacitor (C)
- V = potential difference (V)
- C = capacitance (F)
- If the potential V is substituted, the work done can also be defined in terms of the charge and the capacitance:
Worked example
Calculate the change in the energy stored in a capacitor of capacitance 1500 μF when the potential difference across the capacitor changes from 10 V to 30 V.
Answer:
Step 1: Write down the equation for energy stored in terms of capacitance C and p.d V
Step 2: The change in energy stored is proportional to the change in p.d
Step 3: Substitute in values