Lenz's Law — Why Induction Opposes Change
Part of Electromagnetic Induction — GCSE Physics
This how it works covers Lenz's Law — Why Induction Opposes Change within Electromagnetic Induction for GCSE Physics. Revise Electromagnetic Induction in Magnetism for GCSE Physics with 13 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 14 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 5 of 14
Practice
13 questions
Recall
12 flashcards
⚙️ Lenz's Law — Why Induction Opposes Change
Lenz's law states that the induced current always flows in a direction that opposes the change causing it. This is a consequence of the conservation of energy.
Think of it this way: if the induced current helped the magnet move faster into the coil, you would be getting electrical energy for free — the magnet would accelerate and generate more current, which would accelerate it further. This would violate conservation of energy. Instead, the induced current creates a magnetic field that pushes back against the incoming magnet — you have to do work to push the magnet in, and that work is converted into electrical energy.
Practical implication: This is why generators need mechanical input (wind, steam, water) — the electricity they produce comes directly from the mechanical work done to keep the coil rotating against the opposing force. There is no "free" electricity.
This opposing effect also explains why eddy currents are induced in metal objects moving through magnetic fields — they create braking forces. This is exploited in magnetic braking systems on roller coasters and trains.