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.
Capacitors in series and parallel
RC circuit discharging
Capacitor in a circuit at steady state
General method for capacitance
Capacitance definition
Energy density of an electric field
Partially filled dielectric
Why energy changes when a dielectric is inserted
Capacitance of a spherical capacitor
Energy stored in a capacitor
Dielectric constant
Cylindrical and spherical capacitors
Short answer 1. Define or explain: Force between capacitor plates
3 ptsShort answer 2. Define or explain: RC circuit charging
3 ptsShort answer 3. Define or explain: Charge redistribution between capacitors
3 ptsShort answer 4. Define or explain: Dielectric at constant charge vs constant voltage
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 long straight cylindrical conductor of radius R = 2.0 mm carries a steady current I = 5.0 A distributed uniformly over its cross-section.
State Ampère’s law and use it to derive the magnetic field magnitude at a radius r inside the conductor (r < R).
Derive the field for r > R and evaluate the field at r = 1.0 mm, at r = R, and at r = 6.0 mm.
Describe a graph of B versus r from r = 0 to r = 3R.
A second parallel wire 0.10 m away carries 3.0 A in the same direction. Determine the magnitude of the force per unit length between the wires and state whether it is attractive or repulsive.
The straight wire is replaced by a circular loop of radius 0.050 m carrying 5.0 A. Use the Biot–Savart law to determine the field at the center of the loop, and explain why Ampère’s law is not a convenient tool for this geometry.