Knowledge Organiser: Electromagnetic Induction

Electromagnetic induction: The production of a voltage when there is a changing magnetic field through a conductor
Induced potential difference: The voltage produced in a conductor by a changing magnetic field
AC generator (alternator): A device that converts kinetic energy to AC electrical energy using slip rings
Dynamo: A device that produces DC using a split-ring commutator instead of slip rings
Slip rings: Continuous rings that allow the rotating coil to maintain contact — output is AC
Split-ring commutator: A split ring that reverses the connection every half turn — output is DC
Direction of the induced current (Higher tier): The induced current always flows in a direction that opposes the change that caused it (either the movement of the conductor or the change in the magnetic field)

A voltage is induced only when the magnetic field through the conductor is CHANGING
A stationary magnet in a coil produces NO induced voltage
To increase induced voltage: move faster, use a stronger magnet, use more coil turns
To reverse the current direction: reverse the motion OR reverse the magnetic field
The induced current always opposes the change that caused it, which is why work must be done to drive a generator (conservation of energy)
AC generators use slip rings → continuous contact → alternating current output
DC dynamos use split-ring commutator → reverses connection → direct current output
The National Grid transmits electricity at high voltage so the current is low, which reduces power wasted as heat in the cables
Discovered by Faraday in 1831; used in all power station generators

Always say the magnetic field must be CHANGING — not just that the magnet must move
Slip rings → AC; split-ring commutator → DC (easy to confuse in exams)
The motor effect and induction are opposites: motor = current+field→force; induction = motion+field→voltage
For "Suggest" questions: apply the three factors (speed, field strength, coil turns) to any novel device
For questions on the direction of an induced current: always name what is opposed (the motion of the magnet, or the change in the magnetic field) and link it to conservation of energy

Vs ÷ Vp = Ns ÷ Np (transformer equation — voltage ratio)
Vp × Ip = Vs × Is (transformer power — 100% efficiency)
Induced potential difference increases with: faster movement, stronger field, more coil turns
National Grid: high voltage → low current → less power wasted as heat (power wasted = current² × resistance) in the transmission cables

Saying a stationary magnet induces a voltage: Electromagnetic induction requires a changing magnetic field — the magnet must be moving relative to the conductor for a voltage to be induced
Confusing slip rings and split-ring commutator: Slip rings produce AC (alternating current) in a generator; a split-ring commutator produces DC — don't swap these in exam answers
Getting the transformer equation ratio wrong: Vs/Vp = Ns/Np — more turns on secondary = higher voltage (step-up); fewer turns = lower voltage (step-down)
Forgetting transformers only work with AC: Transformers require a continuously changing magnetic field — they only work with AC, not DC
Confusing motor effect and induction: Motor effect: current + field → force; electromagnetic induction: motion + field → induced voltage — they are reverse processes
Forgetting to name what is opposed: "The induced current opposes the change" is not enough on its own — state what is changing (the magnet's motion or the change in the magnetic field) and that the induced field pushes back against it

Electromagnetic Induction, Knowledge Organiser