Sat March 24, 2012 By: Amit Agarwal

derive capacitance of parallel plate capacitor

Expert Reply
Sat March 24, 2012

Parallel plate model

Dielectric is placed between two conducting plates, each of area A and with a separation of d


The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity ? (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 ±? = ±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 = ?/?. The voltage is defined as the line integral of the electric field between the plates

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

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