CK-12-Physics - Intermediate

http://www.ck12.org Chapter 16. Electric Potential

16.2 Electric Potential

Objectives

The student will:

• Understand how to solve problems using electric potential energy.


• Understand how to solve problems using voltage differences.


• Understand how to solve problems in a uniform electric field.

Vocabulary

• electric potential:Energy per unit charge.


• electric potential difference:The difference in electric potential between two points within an electric field.


• voltage:The amount of work done by the electric field per unit charge in moving a charge between two points
  in the electric field∆V=Wq, also known as a change in potential energy.

Introduction

In order to draw an analogy betweengravitational potential energyandelectrical potential energy, we liken the

electric fieldEto the gravitational accelerationgand the massmof a particle to the chargeqof a particle. Of

course,gis assumed constant (uniform) when we remain close to the surface of the Earth. As of yet, we have not

encountered an example of a uniform electric fieldE.

But that won’t stop us from making a prediction!

Since the gravitational potential energy of a massmin a uniform gravitational field isPEgravity= (mg)h, we predict

the electric potential energy(PEelectric)of a charge(q)in a constant electric field isPEelectric= (qE)h.

Furthermore, theelectric potential(the energy per unit charge) can be defined asVe=PEelectricq (The subscript “e”

will be dropped from now on.) We will discuss electric potential later.

It must be understood that, just as with gravity, the electric potential energy and the electric potential are measured

at the same point. If a point chargeqhas electric potential energyPEx 1 at pointx 1 , the electric potential atx 1 isVx 1

PEx 1 =qVx 1 →Vx 1 =

PEx 1

q

Again, only differences in electric potential and electric potential energy are meaningful. That is,∆PEor∆V→
Vf−Vi=PEqf−PEqi.