19.4 Capacitors

A combination of two metal conductors of same shape, placed close to each other, with one of the conductors being earthed or grounded, is called a capacitor. A capacitor can store more charge than either of the two conductors (from which it is made) taken separately.

Capacity (C)

The amount of charge Q stored in a condenser (Capacitor) is proportional to the P. d. V between the two conductors.

The constant 'C' is called the capacity (capacitance) of the condenser.

In practice 1 mf, 1nf, 1 pf C 10^-6, 10^-9, (10^-K Farad capacities are used as 1 Farad Capacity condenser is of enormous size.)

Parallel plate capacitor and its capacity

Two metal plates (rectangular) identical in all respects and separated by distance 'd' is called parallel plate capacitor.

Within the capacitor, the intensities of the electric field due to a positive Q charge on the left plate and the induced charge -Q on the right plate (which is grounded) are perpendicular and within the same direction.

Since E is uniform (as d<< l, b, l and b are lengths and breadths of plates) between the plates.

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Chapter 20