Unit 5: Magnetic Fields
Physics C: E&M · Unit 5 · Paper 2

Magnetic Fields 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 21 terms and is the same for everyone, so a teacher can assign “Unit 5, 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

Circular motion in a magnetic field

2

Force between parallel wires

3

Ampère's law

4

Why magnetic force does no work

5

Field of a finite wire segment

6

Mass spectrometer

7

Hall effect

8

Torque on a current loop

9

Magnetic dipole

10

Magnetic force on a charge

11

Field of a toroid

12

Force on a current-carrying wire

Short answer 1. Define or explain: Ampère's law vs Biot-Savart

3 pts

Short answer 2. Define or explain: Velocity selector

3 pts

Short answer 3. Define or explain: Field of a long straight wire

3 pts

Short answer 4. Define or explain: Field at the center of a circular loop

3 pts

Free response

10 pts

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.