The Property of Capacitance

ELECTRICAL COMPONENTS CAN OPPOSE THE FLOW OF AC IN THREE WAYS, TWO OF WHICH YOU’VE learned about. Resistance slows the flow of ac or dc charge carriers (usually electrons) by brute force. Inductance impedes the flow of ac charge carriers by temporarily storing the energy as a magnetic field. Capacitance, about which you’ll in these topics, impedes the flow of ac charge carriers by temporarily storing the energy as an electric field.

The Property of Capacitance

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Imagine two huge, flat sheets of metal that are excellent electrical conductors. Suppose they are each the size of the state of Nebraska, and are placed one over the other, separated by only 1 foot of space. If these two sheets of metal are connected to the terminals of a battery, as shown in above figure, they will become charged electrically, one positively and the other negatively.

If the plates were small, they would both become charged almost instantly, attaining a relative voltage equal to the voltage of the battery. But because the plates are gigantic, it will take a little time for the negative plate to reach full negative potential, and an equal time for the other plate to reach full positive potential. Eventually, the voltage between the two plates will equal the battery voltage, and an electric field will exist in the space between the plates. This electric field will be small at first, because the plates don’t charge up right away. But the charge will increase over a period of time, depending on how large the plates are, and also depending on how far apart they are. following figure is a relative graph showing the intensity of the electric field between the plates as a function of time, elapsed from the instant the plates are connected to the battery terminals.

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Energy will be stored in this electric field. The ability of the plates, and of the space between them, to store this energy is the property of capacitance. As a quantity or variable, capacitance is denoted by the uppercase italic letter C.