24.0 - Introduction
In this chapter, we discuss electric potential energy and electric potential.
Understanding these topics will be crucial to your understanding of how electric
circuits and components work. For instance, when you turn on a flashlight, you are
allowing an electric potential difference to drive a current that causes the light bulb
to glow.
In the sections that follow, you will learn how electric charges and fields can create
electric potential energy, electric potential, and electric potential differences. You
may be unfamiliar with the term electric potential difference, but you likely know its
units, volts, and you have probably heard the informal term “voltage” used for it.
The simulations to the right allow you to experiment with electric potential energy.
Just as a configuration of masses, such as a barbell held above the Earth’s surface,
possesses gravitational potential energy, so too does a configuration of electrically
charged particles possess electric potential energy.
The first simulation contains a stationary positive charge (red) and a positive test
charge (white) that you drag around with your mouse. As you move the test charge
from place to place, you can change the electric potential energy of the system of
two charges. The potential energy, which depends on the distance r between the
charges and their strengths, is displayed in the control panel. A graph of the PE is
drawn on the right side of the simulation as you move the test charge around. A grid
in the background of the simulation allows you to estimate the distance in
millimeters between the two charges.
As you move the test charge, consider the following questions: What is the sign of
the PE? When is the potential energy the greatest? The least? The graph shows
PE as a function of the distance r between the charges.
As with gravitational potential energy, a configuration having zero potential energy
must be defined. In the first two interactives, the potential energy is defined to be
zero when an infinite distance separates the two charges.
Interactive 2 is the same as Interactive 1 except that the stationary charge is
negative instead of positive. Experiment with this configuration by moving the
positive test charge around. What is the sign of the PE now? As the distance
increases, does the PE increase or decrease? Can you move the charge in a way
such that the PE does not change?
In the Interactive 3 simulation, you see a test charge that you can move between
two oppositely charged plates. The electric field is uniform between the plates. In
this simulation, the x axis of the graph tells the distance of the test charge from the
negative plate. How does the PE change as you move the test charge away from
the negative plate and toward the positive plate?(^436) Copyright 2000-2007 Kinetic Books Co. Chapter 24