# in parallel plate combination of capacitors charge is variated. why? as wel as in series plate combination of capacitors potential is varied. why?

SAGAR SINGH - IIT DELHI
878 Points
13 years ago

Dear student,

The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity ε (such as air). The model may also be used to make qualitative predictions for other device geometries. The plates are considered to extend uniformly over an area A and a charge density ±ρ = ±Q/A exists on their surface. Assuming that the width of the plates is much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude E = ρ/ε. The voltage is defined as the line integral of the electric field between the plates

$V= \int_0^d E \mathrm{d}z = \int_0^d \frac{\rho}{\varepsilon} \mathrm{d}z = \frac{\rho d}{\varepsilon} = \frac{Qd}{\varepsilon A}.$

Solving this for C = Q/V reveals that capacitance increases with area and decreases with separation

$C= \frac{\varepsilon A}{d}$.

The capacitance is therefore greatest in devices made from materials with a high permittivity.

All the best.

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