CAPACITOR AND CAPACITANCE CLASS 12

 Capacitors 

A capacitor is a device having two metal plates seperated by small distance, these metals have opposite charge. Some dielectric is also introduced between these plates.

• The total charge of a capacitor is zero while the conductors have charge Q and –Q.
• A single conductor can be considered as capacitor with other conductor at infinity.
• Electric field in the region between the conductors is proportional to the charge Q.
• Capacitors is also called condensers.

Types of capacitors

i) Parellel plate capacitor

ii) Spherical capacitor

iii) Cylindrical capacitor

 Capacitance

Capacitance of a conductor is a measure of ability of the conductor to store charge.

when a charge is given to a conductor, it is raised to a certain potential. As charge on the conductor increases its potential rises

i.e         charge  ∝   potential

                  Q     ∝ V

                   Q    =  CV

Where c is capacity of capacitance.

S.I unit of capacitance is farad (F).

Capacitanceis denoted by, C = Q/V. It depends on

• Geometrical configuration (shape, size, separation) of the system of two conductors.
• Nature of insulator/dielectric separating
• Charge on the capacitor leaks away due to reduction in the insulating power of the intervening medium. This happens due to higher potential difference causing strong electric fields.

• Maximum electric field which a dielectric medium can withstand without breakdown and prevent leaking of charge is called dielectric strength. Air dielectric strength is 3 x 106 Vm-1.