Capacitors and Capacitance

Capacitors are used in flash cameras, electronic circuits, power supplies, tuning devices, and energy-storage systems. The source material also emphasises that capacitance depends on geometry and dielectric medium, not merely on the amount of charge stored.

A system consisting of two conductors having equal and opposite charges separated by an insulator or dielectric is called a capacitor.

The ability of a conductor to store charge is called the capacity of conductor.

The ratio of the charge Q given to one of the conductors of a capacitor to the potential difference V between the conductors is called its capacitance, given by C = Q/V.

The maximum electric field that a dielectric medium can withstand without breakdown (of its insulating property) is called its dielectric strength.

C = Q/V

C = 4πkε₀ · [\[\frac {ab}{(b − a)}\]]

C = \[\frac {2πkε₀ l}{2.303 log(b/a)}\]

What capacitance means in simple words

• A larger capacitance means more charge can be stored for the same potential difference.
• Capacitance depends on the size, shape, separation of conductors, and the dielectric medium between them.
• Capacitance does not depend directly on the charge already stored or the applied potential difference.

Real-life analogy

Think of a capacitor like a water tank:

• charge corresponds to water stored,
• potential difference corresponds to pressure, and 
• capacitance tells how much water the tank can hold for a certain pressure.

• SI unit of capacitance: farad (F).
• In practice, capacitors are commonly measured in microfarads, nanofarads, and picofarads.
• A large capacitance means large charge storage at a comparatively small potential difference.

Revision Box: Remember: A good capacitor stores more charge without causing dielectric breakdown. This is why dielectric strength is important.

Capacitance depends on:

• geometry of the conductors,
• size of the conductors,
• distance between them,
• nature of the dielectric medium.

For a given capacitor, capacitance is fixed by construction and material. Changing only charge or potential does not change its capacitance.

Series Combination

• Each capacitor carries the same charge.
• Potential difference across each capacitor may be different.
• The capacitor with smaller capacitance gets a larger potential difference.

Parallel Combination

• Each capacitor has the same potential difference.
• Charges on capacitors may be different.
• This arrangement is used to obtain a larger effective capacitance at a low potential difference.