It was easy to get the first few in but I imagine it got harder and harder. Lets hope nobody had beans for lunch.
Energy Stored
Charging a capacitor is like squashing a spring. You are forcing charge onto the plates where it doesn't want to go because there is charge already on it.
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21 students in Malaysia managed to get into a mini at the same time. It was easy to get the first few in but I imagine it got harder and harder. Lets hope nobody had beans for lunch. |
Remember that a volt is a Joule per Coulomb. When a capacitor is charged to a voltage of say 6V then the power supply has had to do 6J of work to get every coulomb of charge on it.
Does this mean that it stores energy W = Q V?
No. This is how much work the power supply has had to do but some of this energy has been transferred by the resistance in the circuit. half of it in fact.
The energy stored by a capacitor = 1/2 Q V or 1/2 C V2
Example
A 470 µcapacitor is charged to 12V.
Calculate a) the charge stored and b) the energy stored.
Q = C V = 470 x 10-6 x 12 = 5.64 x 10-3 C Energy = 1/2 C V2 = 0.5 x 470 x 10-6 x 144 = 33.8 mJ
Here is a good way of demonstrating that the energy stored is proportional to the voltage squared.