Study Guide: Chapter 28
The Electric Potential
We have talked about forces, and how the electric field is related the force. Now we
move on to energy concepts. Recall in PH211 how you were able to calculate the
work done by a force. You will learn that static electric forces are conservative, so
there must be an electric potential energy – just like there is gravitational potential
energy. We will also define a scalar field called the electric potential in this chapter.
The good news is that you don't have to worry about vector components for electric
potential. Ever heard of voltage? Read chapter 28 to find out more.
The goal of this chapter for you, as a student, is to…
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To introduce electric potential energy and use it in conservation of energy problems.
To define the electric potential.
To find and use the electric potential of point charges, charged spheres, and parallelplate capacitors.
To find the electric potential of a continuous distribution of charge.
To introduce and use potential graphs and equipotential surfaces.
Once you have studied the lecture notes and read the book chapter, can you
answer the following questions?
Section 28.1
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How is force related to the work done by that force?
What is a conservative force?
Can you see the similarites between gravitational potential energy and
electric potenital energy?
What is the electric potential in a uniform field? What is the reference
potential?
Section 28.2
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What is the electric potential energy between two point charges?
Do you know how derive this equation? - the prinicple is useful, and we will
do more of this in chapter 29.
Can you argue, using two point charges, that the electric force is
conservative?
How do you handle multiple point charges?
Section 28.3
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What the potential energy of a dipole?
What does the graph of this potential look like, and can you see that you
could get some oscillation from a dipole in a uniform electric field?
Section 28.4
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What the electric potential?
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At a point P, does it matter what charge you put at the point?
What is the SI unit for electric potential, and who is it name after?
Have you encounted this unit anywhere outside of physics?
How can you use the change in electric potential to calculate the speed of a
charge, and in other conservation fo energy problems?
Section 28.5
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What does the graph of the electric potential look like inside a parallel-plate
capacitor?
Are the contour lines (equipotential lines) of a parallel plate capacitor evenly,
or unevenly spaced?
Name a source of electric potential.
On a capacitor, does it matter at what potential the negative electrode is set?
Section 28.6
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What is the electric potential of a point charge? Can you see how it comes
from the electric potential energy between two point charges?
What is the convetional electric potential for something very far away from a
point charge?
What is the electric potential outside a uniformly charged sphere?
How does the potential at the surface of a uniformly charged sphere relate to
the potential a distance r>R away from the sphere?
Section 28.7
• How do you calculate the potential at a point due to many discrete source
charges?
• How does superposition apply to electric potentials?
• What does the electric potential of the human heart look like?
• Why does it help to think of the electric potential due to positive charges as
mountain peaks, and the electric potential due to negative charges as deep
wells/valleys?
• Can you calculate the electric potential for a continuous distribution of
charge?
◦ How is this different to calculationg the electric field due to a continuous
distribution of charge?
◦ What properties do you look for to define dq?