AP Physics 2: Algebra-Based, AP exams, 12–15%

Unit 12: Magnetism and Electromagnetism

Unit 12 covers magnetic fields, the forces they exert on moving charges and current-carrying wires, and the induction that links changing magnetic flux to induced potential difference. The geometry is three-dimensional, so the right-hand rules need enough practice to become reliable under time pressure.

Position: 4 of 7 units
Published weighting: 12–15% in the official framework
Topics covered: 5 topics in this guide

What is covered

Topics inside this unit.

These topics describe the scope students most often review for this part of AP Physics 2: Algebra-Based. Treat them as a study checklist rather than an exhaustive list of what a single exam form can sample.

Magnetic fields: Field sources, field-line representation, and the difference between magnetic and electric field behavior.
Magnetism and moving charges: The force on a charge moving through a field, its direction, and the resulting circular paths.
Magnetism and current-carrying wires: The field around a straight wire and a loop, and the force between parallel current-carrying wires.
Magnetic flux: Flux as field through an area, and the three ways flux can change over time.
Electromagnetic induction: Induced potential difference from changing flux, and using Lenz's reasoning to find the induced current direction.

Study tips

How to practice Magnetism.

Section-specific guidance that follows from how this material is usually tested.

Drill the right-hand rules daily in short sessions until orientation is instant rather than reasoned out.
For induction problems, identify which of the three flux factors is changing before anything else.
Practice explaining induced-current direction as an opposition to the change, in one written sentence.

Where this fits

Unit 12: Magnetism and Electromagnetism is 4 of 7 units in the AP Physics 2: Algebra-Based guide, and it carries a published weighting of 12–15% in the official framework. Use the full guide to balance it against everything else you have to review.

Back to the AP Physics 2: Algebra-Based guide Official exam information

Sample Magnetism questions

Practice questions, not yet expert-reviewed

Original practice questions written to the published framework for this section. No expert has reviewed them, and they are not taken from any official exam. Try each one before you open the answer.

Question 1Foundational
A proton carrying a charge of 1.6 x 10^-19 C moves at 2.0 x 10^6 m/s perpendicular to a uniform magnetic field of magnitude 0.50 T. What is the magnitude of the magnetic force on the proton?
1. A1.6 x 10^-19 N
2. B8.0 x 10^-14 N
3. C1.6 x 10^-13 N
4. D3.2 x 10^-13 N
Show answer
Answer: C. 1.6 x 10^-13 N
For motion perpendicular to the field, F = qvB = (1.6 x 10^-19)(2.0 x 10^6)(0.50) = 1.6 x 10^-13 N. The 3.2 x 10^-13 N choice leaves out the factor of 0.50 T.
Key insight: The magnetic force is largest when velocity is perpendicular to the field and vanishes when the two are parallel.
Question 2Foundational
A straight wire segment of length 0.40 m carries a current of 5.0 A and lies perpendicular to a uniform magnetic field of magnitude 0.20 T. What is the magnitude of the magnetic force on the segment?
1. A0.10 N
2. B0.40 N
3. C2.5 N
4. D4.0 N
Show answer
Answer: B. 0.40 N
For a wire perpendicular to the field, F = BIL = (0.20 T)(5.0 A)(0.40 m) = 0.40 N. The 2.5 N choice divides by the length instead of multiplying by it.
Key insight: A current-carrying wire in a field feels a force because it is a stream of moving charges.
Question 3Intermediate
True or false: the magnetic force acting on a charged particle that moves through a magnetic field can change the particle's speed.
1. ATrue
2. BFalse
Show answer
Answer: B. False
The magnetic force is always perpendicular to the velocity, so it does no work and cannot change kinetic energy or speed. It changes only the direction of motion, which is why a charge entering a uniform field perpendicular to it travels in a circle at constant speed.
Key insight: Magnetic forces steer charges; electric forces are what speed them up or slow them down.
Question 4Intermediate
A single circular loop of wire with an area of 0.020 m^2 sits in a uniform magnetic field directed perpendicular to the plane of the loop. The field magnitude decreases steadily from 0.30 T to 0.10 T over 0.50 s. What is the magnitude of the emf induced in the loop?
1. A2.0 x 10^-3 V
2. B4.0 x 10^-3 V
3. C8.0 x 10^-3 V
4. D1.6 x 10^-2 V
Show answer
Answer: C. 8.0 x 10^-3 V
Faraday's law gives emf = A(change in B)/(change in t) = (0.020 m^2)(0.20 T)/(0.50 s) = 8.0 x 10^-3 V. The 1.6 x 10^-2 V choice uses 0.40 T by adding the field values instead of subtracting them.
Key insight: Only the rate of change of flux induces an emf, so a strong but steady field induces nothing.
Question 5Advanced
A circular conducting loop lies flat on a horizontal table. A bar magnet is held above the loop with its north pole pointing straight down and is then moved downward toward the loop. Viewed from above, in which direction does the induced current flow around the loop?
1. AClockwise
2. BCounterclockwise
3. CNo current is induced
4. DThe current reverses direction repeatedly
Show answer
Answer: B. Counterclockwise
Field lines leave the magnet's north pole, so the flux through the loop points downward and grows as the magnet approaches. By Lenz's law the induced current opposes that growth by producing an upward field inside the loop, and the right-hand rule then gives a counterclockwise current as seen from above.
Key insight: Lenz's law is conservation of energy in disguise: the induced current always opposes the change that created it.

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Unit 12: Magnetism and Electromagnetism