Electromagnetic Induction — A-Level Physics Revision

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What is Electromagnetic Induction?

Electromagnetic induction is the process of generating an electromotive force (EMF) and hence a current in a conductor by changing the magnetic field around it. This topic is governed by two key laws: Faraday's Law, which states that the magnitude of the induced EMF is proportional to the rate of change of magnetic flux linkage, and Lenz's Law, which states that the direction of the induced current will always be such as to oppose the change that caused it.

Board notes: Electromagnetic induction is a crucial A-Level topic for all boards (AQA, Edexcel, OCR). Faraday's and Lenz's laws are fundamental concepts. Applications such as generators and transformers are covered by all boards, though the level of detail required for transformer inefficiencies (like eddy currents) can vary.

Worked example

Common mistakes

• 1Confusing the roles of Faraday's Law and Lenz's Law. Faraday's Law gives the magnitude of the induced EMF, while Lenz's Law gives its direction. Both are needed for a complete description.
• 2Incorrectly determining the direction of the induced current using Lenz's Law. This requires careful thought about whether the flux is increasing or decreasing and what direction of current would create a magnetic field to oppose that change.
• 3Forgetting that a steady, unchanging magnetic field does not induce an EMF. An EMF is only induced when there is a *change* in the magnetic flux linkage, for example, by moving a magnet relative to a coil or changing the current in an electromagnet.

Electromagnetic Induction exam questions

Exam-style questions for Electromagnetic Induction with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is magnetic flux linkage?

  Magnetic flux linkage is the product of the number of turns in a coil (N) and the magnetic flux (Φ) passing through each turn. It quantifies the total amount of magnetic field 'linked' with the coil.

• How do transformers use electromagnetic induction?

  A transformer uses a changing magnetic field in its iron core, produced by an alternating current in the primary coil, to induce an alternating EMF of a different magnitude in the secondary coil. The ratio of the EMFs is determined by the ratio of the number of turns on the coils.