The formula used to compute the value of capacitance is:

(K A)

C = 0.2249

d

Where C = capacitance in picofarads

A = area of one plate, in square inches

d distance between the plates, in inches

K = dielectric constant of the insulating material

0.2249 = a constant resulting from conversion from metric to

British units.

Example: Find the capacitance of a parallel plate capacitor

with paraffin paper as the dielectric.

Given:

K = 3.5

d = 0.05 inch

A 12 square inches

(K A)

Solution: C = 0.2249

d

(3.5 x 12)

C = 0.2249

0.005

C = 189 picofarads

By examining the above formula it can be seen that capacitance

varies directly as the dielectric constant and the area of the

capacitor plates, and inversely as the distance between the

plates.

e. *Voltage Rating of Capacitors*. In selecting or substituting

a capacitor for use, consideration must be given to both the

value of capacitance desired and the amount of voltage to be

applied across the capacitor. If the voltage is too great, the

dielectric will break down and arcing will occur between the

capacitor plates. When this happens, the capacitor becomes a

shortcircuit and the flow of direct current through it can

cause damage to other electronic parts. Each capacitor has a

voltage rating (a working voltage) that should not be exceeded.

The working voltage of the capacitor is the maximum applied

voltage that can be steadily applied without danger of breaking

down the dielectric. The working voltage depends on the type of

material used as the dielectric and on the thickness of the