The document discusses electric potential and potential energy. Some key points: 1) Electric potential (V) at a point is the work required to move a small positive test charge to that point from infinity without any net external force. 2) Lines of equipotential connect all points of equal electric potential. Charged particles placed at these points will not experience a force or change in potential energy. 3) The electric potential due to a point charge can be calculated using the work done to move a test charge from infinity to that point. Potential increases as distance from the charge decreases. 4) At locations of zero potential, like point P in one example, a field can still exist. A

1. 9.3 – Electric Potential

2. Electric Potential Energy uniform fields
The more we move a
charge from A towards
B, the more Potential
Energy it has.
The Potential Energy
will be equal to the
work done:
This is just like:
Electric Potential Energy Gravitational PE

3. Electric Potential (V) uniform fields
All points in a field have a Potential. It is the energy a coulomb’s worth of
charge would have if placed at that point.
Field Lines
Lines of
Equipotential
1. What’s the Potential Difference (pd) between: a) A & C? b) B & D?
2. If a Charge of +3C is placed at B, how much PE does it have?
3. If a charge of +2C is moved from C to B, how much work would be done? What about -2C?
4. If a charge of +3C was placed at B and released, what would it do? How much KE would it
have at A?

4. Electric Potential definition
Electric Potential (V) at a point is the amount of work per
unit charge needed to take a small positive test charge from
a place of zero potential (infinity) to the point.
Potential Gradient (V) and Field Strength (E)
Uniform Fields:
Just like with Gravitational fields the Electric
Field Strength is the same as the Potential
Gradient for the sort of uniform field you get
between two electrodes.

5. Potential (V)
-
+
+
-
This image shows the
Electric Potential around charges
and draws it as an equipotential surface.
It is easy to see what will happen to a positive charge if
it is placed somewhere on this surface.
Electric Fields and Charges behave just like Gravitational fields and
Masses, the only real difference is that they can attract AND repel.

6. Equipotential simulations
For both simulations click in the drop down box and change it to
equipotential. Then shoose different scenarios to see the equipotential lines
Vector Fields Applet Electrostatics Applet
http://www.falstad.com/vector3de/ http://www.falstad.com/emstatic/
CLICK ON THE PICTURES if the links don’t work

7. Lines of Equipotential (V)
Graphene
The 2010 Nobel prize for Physics was
awarded to Andre Geim and Konstantin
Novoselov of the University of Manchester
(UK) for their experiments with Graphene.
Around graphene atoms there are
‘valleys’ of equipotential that
electrons can flow through, giving the
material really unusual electrical
properties.
If the electron is moving along an
equipotential it is doing no work.
Electrical current with no resistance ?
At room temperature?
Click on the pictures for more info

8. Potential due to a point charge
The Potential at point P is defined as the amount of work per
unit charge needed to take a small POSITIVE test charge
from a place of zero potential (infinity) to P.
P has a +ve
potential (+V)
-W
-Q P has a -ve
potential (-V)

9. Potential due to a point charge continued
The first graph represents the Force as the +ve test charge moves from ∞ to P.
The area under the graph is the Work Done and this allows us to use calculus
to get the Potential (V) graph and Equation.

10. Addition of Potential
Potential is a Scalar
Just add the potential from
each charged body to find
the combined potential.
Extra cleverness
At P there might be zero
potential but that doesn’t mean
there is zero field.
A +ve charge will move to the
right if placed at P so there
must still be a field.