Electric potential definition
“Electric potential at a point in electric field is the amount of work done to bring the unit positive charge from infinity to that point.”
The gravitational potential at point in the gravitational field is the gravitational potential energy of a unit mass placed at that point.In this way ,the electric potential at any point in the electric field is the electric potential energy of a unit positive charge at that point.
If W is the work done in moving a unit positive charge q from infinity to a certain point in the field,the electric potential V at this point is given by:
V = W/q
It implies that electric potential is measured relative to some reference point and like potential energy we can measure only the change in potential between two points.
Electric potential is the scalar quantity.Its unit is volt which is equal to joule per coulomb (J/C).
Definition of volt:
If one joule of work done against electric filed to bring the unit positive charge from infinity to the point in electric field then potential difference at that point will be one volt.
Electric potential energy:
To apply law of conservation of energy,we need to define electric potential energy,potential energy can be defined only for conservative force.The work done by a conservative force in moving an object between any two positions is independent of path taken.The electrostatic force between any two charges is conservative because the dependence of on positions is just like the gravitational force which is conservative force.Hence we can define potential energy for electrostatic force.
We know that the change in potential energy between any two points ,a ans b equals the negative of work done by the conservative force on an object as it moves from point a to point b:
Δ P.E = -W
Hence we define the change in potential energy (P.Eb – P.E a) ,when a point charge q moves from some point a to another point b.As the negative of the work done by the electric force on charge as it moves from point a to b.
For Example,consider the electric field between two equally but oppositely charge parallel plates,we assume their separation is small compared to their width and height,so the field E will be uniform over most of the region as shown in the figure:
Now consider tiny positive charge q placed at point “a” very near to the positive plate.This charge q is so small that it has no effect on electric field E.If this charge q at point a is released ,the electric force will do work on the charge and accelerate it towards the negative plate.Work done by the electric field E to move the charge at a distance d is:
W= Fd =-qed
In this case electric field is uniform.In the case which is illustrated above potential difference decreases, as the charged particle moves from point a to b ,the particles kinetic energy increases by an equal amount.
According to law of conservation of energy,electric potential energy is transformed into kinetic energy,and total energy is conserved.Note that the positive charge q has its greatest potential energy at point a,near positive plate.The reverse is true for a negative charge,its potential energy is greatest near negative plate.
Video about difference between electric potential and electric potential energy: