Capacitors

## Physical description #

All capacitors are thin plates of conductive material separated by a thin layer of insulating material. For the cylindrical electrolytic capacitors in your kit, they are made of two narrow strips of metal foil separated by a strip of thin brown paper, rolled up like a cinnamon roll.

Capacitors behave like frequency-dependent resistors. The governing equation is: $$I = C dV/dt$$ , where $$I$$ is current, $$C$$ is capacitance, and $$dV/dt$$ is the rate at which the voltage is changing. The capacitance is a physical property of a capacitor, and is more or less constant. When the frequency of a signal is high, $$dV/dt$$ is high, so more current flows. This makes the apparent resistance of capacitor low at high frequency. The reverse is also true: a capacitor appears high resistance to low frequency signals.