# 1.09 The effect of the dielectric on the capacitance of the capacitor

Returning back to our analogy with an air pump. One way of describing how the flexible membrane has enabled more air to be transferred, is that it allows the pressure from one chamber, to be applied to the other chamber, to assist the transfer of air.

I.e. the pressure from chamber B, is able to squeeze chamber A, via the flexible membrane, to push more air out. Similarly, the suction of chamber A, expands the volume of chamber B, to pull more air in. The flexibility of the membrane, is a key factor in how effectively these pressures are transmitted from one chamber to another. If the membrane is completely rigid, then no pressure will be transferred between the chambers. The more flexible the membrane is, the greater it will flex and therefore the more effectively, it will transmit the pressures between the chambers.

In a capacitor, the accumulated charge on each plate, creates an electric field that extends to the other plate, “pushing” more electrons off the positive plate and “pulling” more electrons onto the negative plate. This field has to pass through the dielectric and the strength of the field, will depend on the material the dielectric is made of. Permittivity ɛ, is a measure of how easy it is to set up an electric field, within a given material. The higher the permittivity, the stronger the electric field will be. The stronger the field, then the more charge will be accumulated on the plates and therefore the greater the capacitance.

Capacitance is proportional to the permittivity of the dielectric.

C is proportional to ɛ