1
CHAPTER 23
ELECTRIC POTENTIAL
BASIC CONCEPTS:
ELECTRIC POTENTIAL ENERGY
ELECTRIC POTENTIAL
ELECTRIC POTENTIAL GRADIENT –
POTENTIAL DIFFERENCE
6
Now a test charge q0 is placed at position a
a distance ra from q0. Then q0 moves to
position b a distance rb from q0.
What is the change in potential energy?
The change in potential energy is the
negative of the work done to move the test
charge from a to b.
The force on the test charge is
7
The work done is force times distance. But
the force changes as q0 moves away from q
Must integrate
Use
Then
8
The change in potential energy, is the
negative of this work.
DEFINITION:
ELECTRICAL POTENTIAL IS POTENTIAL
ENERGY PER UNIT CHARGE
11
We have as we did at the beginning
The change in potential energy, is the
negative of this work.
Therefore
In Chapter 21 we defined the Electric Field
as the force per unit charge
14
Just like in potential energy of the particle
on a hill we can choose the potential energy
and therefore the potential to be zero at
any arbitrary point.
Choose infinity
In the figure
When
17
The potential at any point in space a
distance from a charge will be
POTENTIALS ADD (SCALERS)
Just as we did with the electric field we can
add the potentials for many charges in an
area.
19
Example 23.11 Potential on axis of ring of
charge.
Choose small segment of ring that has
charge . The segment is a distance
form point P.
Then
21
Use the result to find potential on axis of
disk of charge.
This is diagram for E but use it for finding
potential at P
For ring of radius contribution to V is
22
Disk is made up of rings each with area
Charge density of disk is total charge
divided by total area
Therefore
26
Example
In this chapter we found for ring of charge
In chapter 21 we found for ring of charge
Use equation above for V to find
28
ELECTRON VOLT
An electron volt is a unit for energy. It is
the work necessary to move an electron
(charge ) a potential
difference of 1 volt.
1 Volt Batt
The work to move a charge across a
potential difference is