The diagram shows a parallel plate capacitor with the distance between the plates exaggerated so that the field lines (electric) can be shown clearly.
The capacitance of the arrangement is defined in the equation: . _ charge stored on one plate
capacitance - p0 ten tja| difference between plates
All the lines of force go from the positive charge + Q on the upper plate directly to the negative charge - Qon the lower plate. The number of lines of force is Q / s 0 since there are l / s Q lines of electric force per unit charge. The electric field strength E is the
1111 Area A
number of lines of force per unit area. If the area of the plates is A, then:
X . - _Q_ d Aen
and since C= Q /V
C = EA. d
If the space between the plates is filled with insulating material, the capacitance of the arrangement changes by a numerical factor £r where £r is called the relative permittivity of the insulating substance. The equation for the capacitance becomes:
How this increase in the capacitance comes about is indicated in the diagram below.