Electromagnetic induction (Physics only)

    AQA
    GCSE

    Electromagnetic induction, or the generator effect, occurs when a conductor moves relative to a magnetic field or experiences a changing magnetic field, inducing a potential difference across its ends. If the circuit is complete, an induced current flows, generating a magnetic field that opposes the original change, a manifestation of the conservation of energy known as Lenz's Law. Mastery of this topic requires analyzing the operation of alternators, dynamos, and transformers, and calculating efficiencies in high-voltage power transmission.

    0
    Objectives
    4
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that an induced potential difference is produced when a conductor cuts magnetic field lines or the magnetic field around it changes
    • Credit responses that identify the function of slip rings in an alternator: maintaining a continuous connection to the same side of the coil to produce alternating current (AC)
    • Award 1 mark for explaining that the direction of the induced current opposes the change that produced it (Lenz's Law concept)
    • For transformer calculations, award 1 mark for correct substitution into Vp/Vs = Np/Ns prior to any rearrangement
    • In microphone descriptions, credit the sequence: sound waves cause diaphragm vibration → coil moves in magnetic field → potential difference is induced

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that an induced potential difference is produced when a conductor cuts magnetic field lines or the magnetic field around it changes
    • Credit responses that identify the function of slip rings in an alternator: maintaining a continuous connection to the same side of the coil to produce alternating current (AC)
    • Award 1 mark for explaining that the direction of the induced current opposes the change that produced it (Lenz's Law concept)
    • For transformer calculations, award 1 mark for correct substitution into Vp/Vs = Np/Ns prior to any rearrangement
    • In microphone descriptions, credit the sequence: sound waves cause diaphragm vibration → coil moves in magnetic field → potential difference is induced

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing the operation of a microphone or loudspeaker, use a bullet-point logical flow to ensure you cover the energy transfer and the specific interaction with the magnetic field
    • 💡In transformer questions involving power (VpIp = VsIs), explicitly state the assumption of '100% efficiency' if asked why the equation applies
    • 💡Memorize the visual difference between the oscilloscope traces for an alternator (sine wave) and a dynamo (pulsing DC) to instantly identify the device
    • 💡Always check if the question asks for the 'direction of the induced current' or the 'direction of the force' on the wire; these are opposite interactions

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Confusing the generator effect with the motor effect; students often incorrectly apply Fleming's Left Hand Rule to induction scenarios
    • Stating that 'current is induced' in an open circuit; examiners strictly require 'induced potential difference' unless the circuit is explicitly complete
    • Mixing up the function of split-ring commutators (used in dynamos/DC motors) with slip rings (used in alternators)
    • Inverting the transformer ratio equation, particularly when calculating current rather than voltage

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Explain
    Calculate
    Describe
    Compare
    Suggest

    Ready to test yourself?

    Practice questions tailored to this topic