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CAPACITORS AND DIELECTRICS, Polarisation of dielectric - Coggle Diagram
CAPACITORS AND DIELECTRICS
CAPACITORS
A capacitor is a device that can store energy in the form of electric charge.
It consists of two electrical conductors that are seperated by a distance.The space between the conductors may be filled with vacuum or insulating material called dielectrics.
CAPACITANCE
The ability of a capacitor to store charges is known as capacitance
Capacitance C=q/v
Unit-farad, coulomb/volt
If connected in series ,total capacitance C=c1c2/c1+c2
If in parallel, total capacitance C=c1+c2
*Capacitance of a spherical capacitor= 4πε0R
*Capacitance of a spherical conductor enclosed by an earthed concentric spherical shell= 4πε0(ab/b-a)
*Capacitance of a cylindrical capacitor= 2πε0/(log b/a)
*Capacitance of a parallel plate capacitor=ε0A/d (where A is the area and d is the distance between the plates of the capacitor)
If there are n number of plates alternately connected then, capacitance C=(n-1)ε0A/d
Energy stored in a capacitor U=q^2/2C also, U=1/2 CV^2 and U=1/2 qV
Energy stored in a parallel plate capacitor, U= 1/2ε0 E^2Ad
Energy per unit volume of a parallel plate capacitor=1/2ε0E^2
force of atraction between plates of capacitor=1/2 ε0E^2A
Pressure between the plates=1/2ε0E^2
Dielectrics
These are insulating materials that are filled between the plates of a capacitor to increase capacitance.
Dielectric constant (relative permitivity)= k =εr=C/C0
Gauss's Law in Dielectric- Closed integral D.ds=q
Langevin-Debye Equation- αeff=αe+αi+(P^2/3kT)
Clausius-Mossotti Equation εr-1/εr+2=Nα/3ε0
Polarisation of dielectric
Non polar molecule- Molecules in which centre of gravity of proton and electron coincide.
Polar molecule-the molecules in which the centre of gravity of proton and electron are seperated by a distance.
polar molecules work as dipoles and have dipole moment.
Induced dipoles-if a dielectric with non polar molecule is placed in an electric field,the charge centres get displaced.The molecule is said to be polarised by the field and are called induced dipoles.