# Capacitance

fact
A capacitor is formed whenever two conductors are separated by an insulator, like two charged plates which are held close together but not touching.
fact
Capacitance plays a big factor in circuits; often for delays in circuits, energy storage (like a super short term battery), or volatile memory in computers; and components called capacitors are used to introduce capacitance in circuit designs.
fact
The circuit symbol for a capacitor is:
fact
Capacitors are rated in units of capacitance called "farads". Your typical capacitor in electronics in your home is $$\lt 1 mF$$.
law
Capacitance ($$C$$), charge ($$Q$$) and voltage ($$V$$) are all related with the equation: $$Q = C \times V$$
example

Find the charge in a 2$$\mu$$F capacitor that has a voltage across it of 25V

Using our formula $$Q = C \times V = 2\times 10^{-6} \times 25 = 50\mu$$C Where $$\mu C$$ reads "micro coulombs".
example

How much capacitance is required to store $$40\mu$$C of charge at a voltage of 200V?

Rearranging our formula we get $$C = \frac{Q}{V} = \frac{40 \times 10^{-6}}{200} = 200$$nF
fact
The amount of energy stored in a capacitor is given by the equation: $$W = \frac{1}{2}CV^2$$ Where $$W$$ is the energy in joules, $$C$$ is the capacitance in farads and $$V$$ is the voltage across the capacitor in volts.
practice problems