Unit 3: Conductors, Capacitors, and Dielectrics
Physics C: E&M · Unit 3 · Paper 2

Conductors, Capacitors, and Dielectrics 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.

Paper 1Paper 2Paper 3
Each paper is built from this unit’s 19 terms and is the same for everyone, so a teacher can assign “Unit 3, Paper 2” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.
Suggested time 37 min 34 points0/17 attempted
1

Time constant

2

Partially filled dielectric

3

Why energy changes when a dielectric is inserted

4

RC time constant reasoning

5

Capacitor in a circuit at steady state

6

Dielectric constant

7

Energy density of an electric field

8

Force between capacitor plates

9

Capacitance of a spherical capacitor

10

Capacitance definition

11

General method for capacitance

12

Parallel plate capacitance

Short answer 1. Define or explain: Cylindrical and spherical capacitors

3 pts

Short answer 2. Define or explain: RC circuit discharging

3 pts

Short answer 3. Define or explain: Dielectric at constant charge vs constant voltage

3 pts

Short answer 4. Define or explain: Charge redistribution between capacitors

3 pts

Free response

10 pts

This 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.

Two long horizontal frictionless rails a distance L = 0.40 m apart lie in a uniform vertical magnetic field of magnitude B = 0.50 T. A conducting rod of mass m = 0.20 kg lies across the rails, and the circuit is completed by a resistor R = 2.0 Ω. The rod is given an initial speed v₀ = 6.0 m/s along the rails and then released.

Determine the initial emf and the initial current, and state the direction of the magnetic force on the rod.

Determine the initial magnitude of the rod’s acceleration.

Write the differential equation governing v(t) and show that v(t) = v₀e^(−t/τ) is its solution, identifying τ.

Evaluate τ and the speed at t = 5.0 s.

Determine the total energy dissipated in the resistor and the total distance the rod travels, and explain why the rod never quite stops in finite time.