The property of capacitance

Imagine two very large, flat sheets of metal such as copper or aluminum, 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 just a foot of space. What will happen if these two sheets of metal are connected to the terminals of a battery, as shown in Fig. 1?
The two plates will become charged electrically, one positively and the other negatively. You might think that this would take a little while, because the sheets are so big. This is an accurate supposition.
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,

Figure 1: huge pair of parallel plates illustrates the principle of capacitance.

it will take awhile for the negative one to “fill up” with electrons, and it will take an equal amount of time for the other one to get electrons “sucked out.” Finally, however, the voltage between the two plates will be equal to the battery voltage, and an electric field will exist in the space between the plates.
This electric field will be small at first; the plates don’t charge 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. Figure 2 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.

Figure 2: Relative electric field intensity between the huge metal plates, as a function of time.

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. It is denoted by the letter C.