The questions are on the electromagnetic induction test. Take it under real conditions before reading the mark scheme.
Quick answer: Electromagnetic induction is the creation of an emf in a circuit when the magnetic flux linked with it changes. This mark scheme gives the model answers and the marks for the 8 questions of the Physics 11-12 test on electromagnetic induction, from defining flux to falling magnet, with the equivalent answers to accept.
Award marks for method as well as for the final answer. Accept answers within rounding and follow through an earlier slip. Do not penalise a missing unit more than once in each question.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB D.4
Question 1 Defining flux (2 marks)
Magnetic flux is the product of the flux density and the area, with the cosine of the angle between the field and the normal: Φ = BA cos θ. Its unit is the weber (T m²).
Marking: 1 mark for the definition, 1 mark for the unit.
Question 2 Tilted coil (2 marks)
Φ = BA cos θ = 0.25 × 0.030 × cos 40° = 5.7 × 10⁻³ Wb (5.7 mWb).
Marking: 1 mark for substitution, 1 mark for answer with unit.
Question 3 Faraday’s law (3 marks)
a) The induced emf is proportional to the rate of change of flux linkage.
b) ε = NΔΦ/Δt = 400 × 3.0 × 10⁻³ / 0.15 = 8.0 V.
Marking: a) 1 mark. b) 1 mark for substitution, 1 mark for answer.
Question 4 Lenz’s law (3 marks)
a) A south pole, which attracts the receding north pole.
b) The induced current opposes the motion, so work must be done to pull the magnet away. This work is transferred to electrical energy in the coil. If the effect helped the motion, energy would be created from nothing.
Marking: a) 1 mark. b) 1 mark for opposing the motion, 1 mark for work done becomes electrical energy.
Question 5 Sliding rod (3 marks)
ε = BLv = 0.35 × 0.45 × 1.8 = 0.28 V. I = ε/R = 0.2835 / 0.20 = 1.4 A.
Marking: 1 mark for the emf, 1 mark for the formula for I, 1 mark for the answer.
Question 6 Reading a generator graph (3 marks)
a) Peak emf 12 V; period 20 ms.
b) f = 1/T = 1 / 0.020 = 50 Hz; ω = 2πf = 314 rad/s.
Marking: a) 1 mark. b) 1 mark for f, 1 mark for ω.
Question 7 Open and closed coil (2 marks)
In a closed coil an induced current flows. By Lenz’s law it produces a field that opposes the approach of the magnet, so extra work must be done. In an open coil no current flows, so there is no opposing force.
Marking: 1 mark for induced current, 1 mark for opposing force and extra work.
Question 8 Falling magnet (2 marks)
The magnet is accelerating under gravity, so it moves faster as it leaves. The flux changes more rapidly, so ΔΦ/Δt and the emf are larger.
Marking: 1 mark for faster at exit, 1 mark for larger rate of change of flux.
