Edexcel International A Level Physics
Edexcel International A Level Physics Electric and Magnetic Fields Exam Questions
Free Edexcel International A Level Physics exam questions for Electric and Magnetic Fields, with a mark scheme for every pack. Covers uniform and radial electric fields, Coulomb's law, electric potential, capacitors, magnetic forces on currents and charges, and electromagnetic induction.
Electric and Magnetic Fields exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel International A Level Physics Electric and Magnetic Fields
Electric and magnetic fields is part of Unit 4: Further Mechanics, Fields and Particles in Edexcel International A Level Physics. It covers electric fields between parallel plates and around point charges, Coulomb's law and electric potential, then capacitors, the energy they store and their exponential charging and discharging. The magnetic part covers forces on current-carrying conductors and moving charges, magnetic flux and flux linkage, and Faraday's and Lenz's laws. It builds on Electric circuits from Unit 2 and is needed for particle accelerators and detectors. Examiners like capacitor discharge calculations and explanations using Lenz's law.
What you need to know
- Electric fields E = F/Q; between parallel plates E = V/d; radial field E = kQ/r^2 where k = 1/4πε0. Coulomb's law F = kQ1Q2/r^2. Electric potential V = kQ/r; equipotentials are perpendicular to field lines.
- Capacitance C = Q/V. Energy stored W = ½QV = ½CV^2 = ½Q^2/C, the area under a graph of V against Q.
- Charging and discharging During discharge through a resistor, Q = Q0 e^(-t/RC), with similar equations for V and I. The time constant RC is the time to fall to 37% of the initial value; ln Q against t has gradient -1/RC.
- Magnetic forces F = BIl sin θ on a conductor and F = Bqv sin θ on a moving charge, with direction from Fleming's left-hand rule.
- Electromagnetic induction Flux Φ = BA cos θ; flux linkage NΦ. Faraday's law ε = -d(NΦ)/dt; Lenz's law states the induced e.m.f. opposes the change causing it.
Common mistakes in Electric and Magnetic Fields
- Using kQ/r^2 for potential. Potential is kQ/r; field strength is kQ/r^2.
- Using W = QV for capacitor energy instead of ½QV.
- Treating the time constant as the time to discharge completely.
- Forgetting N when calculating e.m.f. in a coil.
- Using the right-hand rule to find the direction of the force on a current-carrying wire. Use Fleming's left-hand rule.
Try three Electric and Magnetic Fields exam-style questions
1. A 220 μF capacitor discharges through a 100 kΩ resistor. Calculate the time constant and the time for the charge to halve. (3 marks)
Show the mark scheme answer
RC = 100 × 10^3 × 220 × 10^-6 = 22 s; t½ = RC ln 2 = 22 × 0.693; t½ = 15 s.
2. Calculate the electric field strength 0.20 m from a point charge of 5.0 μC. (2 marks)
Show the mark scheme answer
E = kQ/r^2 = 8.99 × 10^9 × 5.0 × 10^-6/0.20^2; E = 1.1 × 10^6 N C^-1.
3. Explain, using Lenz's law, why work must be done to push a magnet into a coil connected to a closed circuit. (3 marks)
Show the mark scheme answer
Moving the magnet changes the flux linkage so an e.m.f. and current are induced; by Lenz's law the induced current produces a magnetic field opposing the motion (a like pole facing the magnet); a force must act against this repulsion so work is done, which becomes electrical energy, consistent with conservation of energy.
Electric and Magnetic Fields FAQs
What does Edexcel International A Level Physics Electric and magnetic fields cover?
It covers electric fields and Coulomb's law, electric potential, capacitors and exponential discharge, forces on currents and moving charges, magnetic flux, and Faraday's and Lenz's laws.
Which unit is Electric and magnetic fields examined in?
It is examined in Unit 4: Further Mechanics, Fields and Particles.
What equations do I need for Electric and magnetic fields?
Learn E = F/Q, E = V/d, F = kQ1Q2/r^2, V = kQ/r, C = Q/V, W = ½CV^2, Q = Q0 e^(-t/RC), F = BIl sin θ, F = Bqv sin θ and ε = -d(NΦ)/dt.
