Download Physics Lecture #28

Mon. Feb. 9 – Physics Lecture #28
Electric Potential
1. Electric Work & Electric Potential Energy
2. Electric Potential Energy and Electric Potential
3. Electric Potential due to Point Charges
4. Electric Potential and Electric Field
Vocabulary Pile-Up Warm-Up: Discuss with your neighbors.
Discuss and distinguish between
Electric Charge
Electric Force
Electric Field
Electric Work
Electric Potential Energy
Electric Potential
Electric v. Electrostatic
ConceptCheck: Would a free electron move towards higher potential or lower
(electric) potential?
1. Move towards higher potential
2. Move towards lower potential
3. Neither
4. Not enough information to decide
ConceptCheck: An electron and a proton are each accelerated from rest
through a potential difference of 9 V. Consider the following choices:
1. Electron
2. Proton
3. Same
4. Not enough information
a) Which has the larger final kinetic energy?
b) Which has the larger final speed?
A proton passes point A, traveling with
speed 3 x 104 m/s to the right. A uniform
electric field of magnitude 4.7 x 103 V/m
points to the left. Describe the subsequent
motion of the proton, qualitatively and
quantitatively.
A uniform electric field of magnitude 5 kV/m points
to the right. Consider points A, B, and C as
shown.
E = 5 kV/m
C
a) Determine DVAB = VB – VA
b) Determine DVBC = VC – VB
c) Determine DVCA = VA – VC
2m
B
2m
A
ConceptCheck: Consider the positive
point charge shown in the figure.
What is the potential difference going
from point A at distance a to point B
at distance b?
B
q
b
+
1. 0
 1 1
 a b
4. kq  
 1 1
 a b
2. kq  
 1 1
 a b
3.  kq  
 1 1
b a
5. kq  
6. Can’t be determined
without knowing q.
a
A
Consider four identical point charges –q held fixed
at the corners of a square of side length d as
shown in the figure.
a) What is the electric field at the center of the
square?
b) What is the electric potential at the center of the
square (with respect to infinity)?
A fifth identical particle is placed at the center of
the square and released from rest.
d
-
-
-
-
d
A solid conducting sphere with radius 0.03 m has a net
charge of +2 mC. Assume the sphere has reached static
equilibrium and that there are no other charges around.
a) Plot the magnitude of the electric field as a function of
the distance from the center r.
b) Plot the electric potential as a function of the distance
from the center r.
0.03 m
For some charge configuration, the potential as a function of position in a region
is given by:
V(x)  3x  2x 2  x 3
Where V is in volts when x is in meters. Determine the maximum magnitude of
the electric field associated with this potential.