NEET Physics Notes Electrostatics-Electric Dipole
Electric Dipole
Electric Dipole
An electric dipole consists of two equal and opposite charges separated by a small distance.
The dipole moment of a dipole is defined as the product of the magnitude of either charges and the distance between them. Therefore, dipole moment
p = q(2a)
Dipole moment is a vector whose direction is from negative to positive charge. Its SI unit is coulomb-metre Cm and has the dimensional formula is [LTA].
Electric Field due to a Dipole
Torque on a Dipole in a Uniform Electric Field
When a dipole is placed in an external electric field, making an angle 0 with the direction of the uniform electric field E, it experiences a torque given by
Work Done
If an electric dipole initially kept in an uniform electric field E, making an angle θ1 is rotated so as to finally subtend an angle θ2 then the work done for rotating the dipole is,
Potential Energy of a Dipole
It is the amount of work done in rotating an electric dipole from a direction perpendicular to electric field to a particular direction.
Hence,
Obviously potential energy of an electric dipole is a scalar quantity. It is measured in Joule.
Electric Flux (φE)
Electric flux is a measure of the flow of electric field through a surface. Mathematically, electric flux is the product of an area element ds and the normal component of E, integrated over a surface,
where, n is the unit vector normal to area element ds. Electric flux is a scalar quantity having SI unit as Nm2C-1or V-m. Its dimensional formula is [ML3T-3A-1].
Gauss’s Law
According to Gauss’s law in electrostatics, the total electric flux linked with a closed surface is 1 equal to
times, the net charge eo enclosed by that surface. Thus,
where
is the algebraic sum of all the charges inside the closed surface.
Any closed surface, real or hypothetical, for which the Gauss’s law is applied, is called a gaussian surface.
If a charge Q is placed at the centre of a cube, then the electric flux from the entire surface of the cube is 
, and the electric flux from any one face of the cube is 