Physics - Capacitors
Capacitors are devices designed to store electrical charge. They are
used in situations where electricity needs to be temporarily stored and
then released. A capacitor may be used alongside an electric motor to
provide a brief burst of high current to overcome the friction involved in
starting the motor turning. Once a motor is turning, keeping it moving
often requires far less current. In this section we will look at how
capacitors store charge and release it at the correct time to smooth out
dips in the size of a current flowing in particular circuits.
Capacitors essentially consist of two metallic plates separated by some
type of electrically insulating material. The simplest capacitors use air
as the insulating material but these are limited in the amounts of charge
that they can store. Capacitors storing larger amount of charge establish
the insulator chemically. If a capacitor is not wired correctly into a
circuit a large amount of heat is produced, causing the capacitor to
explode. The plates of a capacitor are often rolled into a cylinder, giving
the capacitor its common form as shown below. The leads are usually
labelled positive and negative but if not, the convention is that the
longer lead is the positive one.
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