Faraday's law test with answers for AP Physics C (free PDF download)

Quick answer: Faraday's law states that a changing magnetic flux through a coil induces an emf equal to −N dΦ/dt, with its direction set by Lenz's law. This AP Physics C test on faraday's law has 8 questions worth 20 marks, to do in 40 minutes: Lenz’s law, flux and emf and solenoid inductance. The mark scheme is on a separate page; free printable PDF.

This test covers Faraday’s law, inductance, LR circuits and LC oscillations. It has 8 questions worth 20 marks. Calculators are allowed and no hints are given.

Level: AP Physics C (Mechanics and E&M, calculus-based) · Curriculum: AP PC:E&M Unit 13

Time: 40 minutes · 8 questions · Total: 20 marks · Calculator allowed

Contents

Question 1 Lenz’s law (2 marks)

A bar magnet is pushed north pole first towards a flat coil.

State the polarity of the face of the coil nearest the magnet. (1 mark)
Explain, using energy, why the polarity must be this way. (1 mark)

Question 2 Flux and emf (3 marks)

A coil of 60 turns and area 8.0 × 10⁻³ m² has B perpendicular to it with B(t) = 0.20 t² tesla (t in seconds).

Write an expression for the emf magnitude. (1 mark)
Calculate it at t = 1.5 s. (2 marks)

Question 3 Solenoid inductance (2 marks)

A solenoid has N = 500, ℓ = 0.25 m and A = 3.0 × 10⁻⁴ m².

Calculate L. (1 mark)
Calculate the emf when the current falls at 80 A/s. (1 mark)

Question 4 LR rise (3 marks)

L = 0.60 H, R = 30 Ω, ε = 6.0 V.

Calculate τ. (1 mark)
Calculate the current at t = 40 ms. (2 marks)

Question 5 Energy store (2 marks)

The circuit in Question 4 reaches steady state.

Calculate the final current. (1 mark)
Calculate the energy stored in L. (1 mark)

Question 6 Explaining the delay (2 marks)

A student closes a switch in a circuit with a large inductor and a lamp, and the lamp brightens slowly. Explain this delay using the idea of induced emf. (2 marks)