Capacitance

Materials store charges by virtue of their capacitance. This can be likened to how most insects
collect food in the summer for winter storage. This storage of charges has made a lot of
technologies possible, especially those that require a temporary storage of charges to function.

Capacitors
A capacitor is a circuit component that temporarily stores charges within the circuit. Inside it are
two conducting plates facing each other and separated by an insulator referred to as a dielectric.
This material impedes the continuous passage of electric current through the capacitor and stores
it until it is discharged at a later time.

Capacitors are constructed by inserting an insulator to form a gap along the path of a conductor.
The size of this insulator affects the amount of charges stored in the capacitor. The junction
between the conductor and the dielectric in a capacitor can be adjusted so the amount of charges
that can be stored by the capacitor may vary. This will be discussed later in this module. This
junction is in the form of a plate to accommodate and hold the dielectric in place. Aside from the
distance between the conductor and the insulator, changing the diameter of the conducting plates
also changes the amount of charges that the capacitor can store.

The amount of charges stored in a capacitor per unit of electric potential is referred to as
capacitance. Mathematically, it is computed using the following equation: C=Q/V

In this equation, Cis the capacitance of the capacitor, Q is the magnitude of the charge stored on
each plate, and Vis the voltage applied to each plate. The unit used to measure capacitance is
coulomb per volt (C/V) or farad (F).

A capacitor's capacitance is dependent on various factors. Table 5.1 summarizes these factors and
their respective effects to the capacitance of a capacitor.
In table 5.1, you can see that the varying area of the conducting plates of the capacitor affects the
capacitance offered by the capacitor. Increasing the area of the plates increases the capacitance,
whereas decreasing the area lowers the capacitance.
The area of the capacitor plate dictates the amount of dielectric that can be inserted in the
capacitor. Because the amount of dielectric provides the area for the storage of charges, increasing
the amount of dielectric also increases the amount of charges that can be stored. This means
increasing the area of the capacitor plates will also increase the capacitance of the capacitor, and
vice versa.

Because the amount of dielectric directly affects the capacitance of the capacitor, increasing the
distance or area between the capacitor plates by inserting more dielectric will also increase the
amount of charges that can.be stored in the capacitor. Placing the plates at a closer distance to
each other will decrease the amount of dielectric between these plates, which consequently
decreases the capacitance.
The role of a dielectric inserted between the capacitor plates is to impede or block the charges
passing through the material. This means that a dielectric has to be made of insulating or less
conducting materials to provide greater capacitance. Greater insulation allows more charges to be
stored. Conducting materials simply allow electric current to pass through them, and no charges are
stored; thus, capacitance is at a minimum.

Although the dielectric impedes the passage of current through the capacitor for storage, small
amounts of current, referred to as leakage current, manages to pass through it. An increase in the
supplied voltage to the capacitor increases the amount of leakage current. Once the supplied
voltage is greater than the breakdown voltage (or maximum voltage) of the capacitor, the capacitor
ceases to store charges and just becomes a conductor.

Every charge carries with it an amount of energy that enables it to move and deliver electrical
current to the load where this energy is needed. If these charges are stored in the dielectric of a
capacitor, the energies that these charges contain are also stored inside the capacitor. This implies
that storing greater amount of charges in the capacitor results in greater energy stored inside it.
This energy is in its potential form; it is waiting to be discharged by the capacitor.

Shape of Capacitors
Capacitors can be classified in terms of their construction-parallel-plate, spherical, and cylindrical.
Each of these has advantages and disadvantages based on capacitance, charge, and potential
difference.

Parallel-plate capacitors are the simplest to understand in terms of construction because they
conform directly to the definition of a capacitor. In this type of capacitor, two parallel charging
plates are separated by a dielectric that contains the charges. The capacitance that can be offered
by a parallel-plate capacitor is directly proportional to the area of the plates as well as to the
distance between these plates. The voltage across this type of capacitor is also directly
proportional to the distance between the plates.

Cylindrical capacitors have a different construction compared to a parallel-plate. As seen in figure

The capacitance of a cylindrical capacitor varies directly with its length. A longer capacitor provides
higher capacitance, whereas a shorter one provides a lower value. Increasing the amount of
dielectric in this type of capacitor also increases the capacitance that it offers. Also, a large or "fat"
cylindrical capacitor offers a higher capacitance than a thin one. Such variation means that an
increase in the distance between the two charged cylinders will increase the amount of work to be
done to move a charge from one cylinder to the other, thereby increasing the voltage across the
capacitor.

Last, spherical capacitors have a construction similar to that of a cylindrical capacitor: As seen in
figure 5.5, an internal spherical structure is one of the charged bodies of the capacitor. The other
charged body is the outer spherical structure that covers the internal sphere. The dielectric is
placed between these two charged spheres.

The capacitance of a spherical capacitor varies directly with its overall radius. Increasing the radius
of this type of capacitor will enlarge the spherical surfaces, consequently widening the distance
between the two charged spheres. By doing so, the amount of dielectric also