ELECTRIC POTENTIAL

ELECTRIC POTENTIAL

Electric potential energy is the energy stored in an electric field. The change in potential energy when objects move around is equal in magnitude but opposite in sign to the work done by the field.

The electric force and electric potential energy for a pair of point of particles are proportional to the product of the charges of the particle

Figure 1: Electric Potential Energy

The charge of particles moves causing the electric potential energy changes. Just like mass in a gravitational field has gravitational potential energy, charges in an electric field have an electric potential energy. A charge’s electric potential energy store amount of energy it has. When set into motion by an electrostatic force, that energy can become kinetic and the charge can do work.

If the:

Two charges have opposite sign:

•                 Attract each other
•                Potential energy should be negative as the    is negative

Figure 2: Opposite Charges Attract

If the:

Two charges have same signs (either both positives or both negatives):

• ·         Repel each other

·         Potential energy should be positive as the    is positive

     

Figure 3: Same Charge Repel

ELECTRIC POTENTIAL DIFFERENCE

Potential differences are the changes in electric potential energy per unit charges

The electric force on charge is always directed toward regions of lower electric potential energy. For a positive charge, lower potential energy means lower energy but for a negative charge, lower potential energy means higher potential. This is because the force on a negative charge is opposite to the direction of E while the force on a positive charge is in the direction of E.

The magnitude of electric potential energy, V is

The unit of electric potential difference is or volts (V)

When a point charge, q moves from point A to point B, it moves through a potential difference

Video 1: Electric Potential Energy

EQUI-POTENTIAL SURFACES

All point on a equi-potential surface have the same electric potential. The electric potential V due to a point charge of +Q is 

The equi-potential surfaces are right angles to the electric field, E. No work is done in moving charge from one point to another point on the same equi-potential surface. For the same difference in electrical potential, the separation between equi-potential surfaces around a point charge increases as r increases.

Equi-potential surfaces and field lines are closely related. As long as the charge is moving in a direction perpendicular to the field, the work done by the field is zero and the potential stays the same. If you want to move a charge in a direction that maximizes the change in potential, you would move parallel or anti-parallel to the electric field.

The electric field is sometimes called the potential gradient.