Electric Potential unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
Potential inside a conducting sphere
Why field is the negative gradient
Electron volt
Relation between field and potential
Energy of assembling charges
Work and potential difference
Potential inside a uniformly charged insulating sphere
Potential energy of a charge pair
Why potential is easier than field
Field from a graph of V vs x
Electric potential of a point charge
Sign of the potential integral
Short answer 1. Define or explain: Field and potential can be independently zero
3 ptsShort answer 2. Define or explain: Potential from a graph of E vs x
3 ptsShort answer 3. Define or explain: Equipotential surfaces
3 ptsShort answer 4. Define or explain: Accelerating a charge through a potential difference
3 ptsFree response
10 ptsThis course has no free-response prompt tagged to this unit, so one from elsewhere in the course is used. It is still worth writing — the skill transfers.
A solid insulating sphere of radius R = 0.20 m carries a total charge Q = 6.0 μC distributed uniformly throughout its volume.
Use Gauss’s law to derive expressions for the magnitude of the electric field at radius r for r < R and for r > R.
Evaluate the field at r = 0.10 m, at r = R, and at r = 0.40 m.
Describe a graph of E versus r from r = 0 out to r = 3R, identifying where the field is greatest.
Using V = −∫E·dl with V = 0 at infinity, derive the potential at the surface and at the center of the sphere, and evaluate both.
Explain how the field and potential expressions would change if the sphere were instead a conductor carrying the same total charge.