Storax

Meet Storax, a capacitor who stores energy in an electric field.

A capacitor is two conductors separated by an insulator. Charging it moves charge from one side to the other, and each extra bit of charge must be pushed against the voltage that has already built up. The work done is stored in the electric field between the conductors.

The stored energy is U = ½CV², where C is the capacitance in farads and V is the voltage. A 100 μF capacitor charged to 10 V stores U = 0.5 × 0.0001 × 10² = 0.005 J. Charge it to 20 V and it stores 0.02 J, four times as much, because the voltage is squared.

Capacitors can release their energy very quickly, which makes them useful for camera flashes, defibrillators and smoothing power supplies.

Because they can hold a dangerous charge even after a device is switched off, large capacitors should be discharged safely before anyone works on the circuit.