Capacitors and Inductors
What are capacitors?
A capacitor is a passive component (it does not have its own source of power) used to store energy in the form of an electric field which resists changes in voltage across its terminals.
How does a capacitor work?
Typically, a capacitor is made up of two conductors (ex. metal plates) separated by an insulator called a dielectric (ex. ceramic). When a power supply, such as a battery is connected to the capacitor, electrons flow from the negative terminal of the battery towards one of the conductors of the capacitor. At the same time, electrons that were already on the other conductor are attracted to the positive terminal of the battery. As a result, there is a build up of negative charge on one conductor and positive charge on the other. This potential difference between the two conductors of the capacitor creates an electric field directed from one conductor to the other. When the capacitor is completely charged, the potential difference across it is the same as that of the supply and no more current flows through the circuit. Furthermore, the capacitor can now act as a power source and therefore, supply energy to the circuit. To see how a capacitor works, see the animation below.
What are inductors?
An inductor is a passive component, meaning it does not have its own source of power. Inductors can store energy in the form of a magnetic field and also resist changes in the amount of electric current flowing through them.
How does an inductor work?
An inductor is simply a coil of conductive wire. Current flowing through the coil builds up a magnetic field. When the current flowing through the inductor changes, the magnetic field induces a voltage change in the circuit that opposes the change in the current. As a result, the magnetic field stores current for a short duration following the cease of current flow in the circuit.
The animation below helps to show how a capacitor can store and release electrical charge. When there is a flow of electrons in the circuit, electricity is being supplied to the light bulb, which causes it to turn on. When the battery is removed, the potential difference across the capacitor causes the electrons to rapidly flow towards the other plate causing the light bulb to, again, light up for a brief period. One of the applications of a capacitor is for devices that require pulses of power, for example, the flash of a disposable camera.
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