Homework Help: Electric Potential, and Potential Difference

Yeah if you go from point A ---> point B, and you've got a potential of 100V at point A and 0V at point B, then the potential difference is B - A = 0V - 100V = -100V.

Electric potential is a value that tells you about a point in space. You can think of it as a "property" that is describing the electric field at a point. At point A the electric potential is 100V, it doesn't matter what kind of charge you put at that point, the electric potential at point A is always 100V.

Electric potential energy is a value that you use to describe the charged objects in electric fields. At point A, the electric potential energy of a charged object would be some number of eV (electron volts, a unit of energy). It depends on the electric potential, and thus the electric field, but it is a property of a given charged object in a field.

Electric potential describes points in a field. Electric potential energy describes objects in a field.

 

The potential difference of point a relative to point b, is determined by the force that the electric field exerts on a unit positive charge multiplied by the distance from a to b x the cosine of the angle between the direction of force and the distance. If you know calculus:

[tex]V = \int_a^b \vec{E}\cdot d\vec{s}[/tex].

The potential energy of a charge at a given point in an electric field has no meaning by itself. It only has meaning in reference to another point. So the only thing that matters is the potential difference. You can arbitrarily set one point at 0 if you like.

In order to determine the sign of the potential difference you have to use the force on a positive charge. So, for example, if the field pushes a positive charge from a to b the potential difference from a to b is positive. If you have to push the positive charge from a to b, the potential difference will be negative.

AM