CAPACITOR

 CAPACITOR

Capacitor is also called a condenser and is a linear passive circuit element, which has the capacity to store energy in the form of an electrical charge and produce a potential difference across its terminals.

Symbol

A capacitor basically consists of two parallel metal plates that are electrically separated by a distance d in meters with dielectric material between the plates.the most common types of dielectric material used are air,polyster, paper,poly propylene, mylar,ceramic,glass,oil

                            C= €A/d Faraday

Where k=€0€r

€0=permittivity of free space=8.854×10-12F/M

K=relative permittivity of the dielectric material between the plates

Example problems 

In the parallel plate condenser,the plates are separated by a distance of 0.1 cm and the area of the plates of the is 100 cm2 .express C in pf, if the dielectric medium is air.

Answer:

€=€0€r=8.854×10-12×0.91m2/0.001m

             =88.54pF

The current in a capacitor is directly related to the charge on the plates.as current is the rate of flow of charge with respect to time and Q is proportional to the applied voltage V,then

                     I=Cdv/dt

The energy stored in a capacitor is the integral of the Istanbul power. assuming that the capacitor had no charge across its plates at t=-infinity,then the energy stored in the capacitor at time t is

       E=1/2CV2

Capacitor in parallel:

When capacitor C1 and C2  are connected in parallel then the effective capacitance Ceq is calculated as follows

I=I1+I2

=C1dv/dt +C2dv/dt

=C1+C2(dv/dt)

=Ceqdv/dt

Where Ceq=C1+C2

Capacitor in series:when capacitor C1 and C2 are connected in series then the effective capacitance Ceq is

dv/dt=d(V1+V2)/dt

          =    dv1/dt+dv2/dt

         1/ceq  =  1/C1+1/C2

Types of capacitor 

1.delectric capacitor 

2.film capacitor 

3.ceramic capacitor 

4.electrolytic capacitor 

Symbol of types of capacitor 

Characteristics of capacitors

1.the normal value of the capacitor C of a capacitor is marked on the body of the capacitor as number, letters,or colored bands

2.toleranance is the range over which the value of C is allowed to vary from its nominal value and is expressed as 10 percent or so. Thus,the value of a 100uF capacitor with 20 percent  tolerance could lie anywhere between 80uF and 120UF.

3.the temperature coefficient of a capacitor is the maximum charge in its capacitance over a specified range of temperature and its expressed as a parts per million per Degree centigrade.