Physics C Electricity and Magnetism

Unit 2: Electric Potential

Big Ideas:
1. Electric potential is electric potential energy per unit charge.
2. Electric field is a measure of how quickly electric potential changes with position.
3. All excess charge resides on the surface of a conductor.
4. Conductors in electrostatic equilibrium are equipotential.
5. The electric field inside a conductor in electrostatic equilibrium is zero.

1. Students should understand the concept of electric potential, so they can:
A. Determine the electric potential in the vicinity of one or more point charges.
B. Calculate the electrical work done on a charge or use conservation of energy to determine the speed of a charge that moves through a specified potential difference.
C. Determine the direction and approximate magnitude of the electric field at various positions given a sketch of equipotentials.
D. Calculate the potential difference between two points in a uniform electric field, and state which point is at the higher potential.
E. Calculate how much work is required to move a test charge from one location to another in the field of fixed point charges.
F. Calculate the electrostatic potential energy of a system of two or more point charges, and calculate how much work is required to establish the charge system.
G. Use integration to determine electric potential difference between two points on a line, given electric field strength as a function of position along that line.
H. State the general relationship between field and potential, and define and apply the concept of a conservative electric field.

2. Students should know the fields of highly symmetric charge distributions, so they can derive expressions for the electric potential as a function of position.

3. Students should understand the nature of electric fields in and around conductors, so they can:
A. Explain the mechanics responsible for the absence of electric field inside a conductor, and know that all excess charge must reside on the surface of the conductor.
B. Explain why a conductor must be an equipotential, and apply this principle in analyzing what happens when conductors are connected by wires.
C. Show that all excess charge on a conductor must reside on its surface and that the field outside the conductor must be perpendicular to the surface.

4. Students should be able to describe and sketch a graph of the electric field and potential inside and outside a charged conducting sphere.

5. Students should understand induced charge and electrostatic shielding, so they can:
A. Describe the process of charging by induction.
B. Explain why a neutral conductor is attracted to a charged object.
C. Explain why there can be no electric field in a charge-free region completely surrounded by a single conductor, and recognize consequences of this result.
D. Explain why the electric field outside a closed conducting surface cannot depend on the precise location of charge in the space enclosed by the conductor, and identify consequences of this result.