Lenz's law states that the induced current always flows in a direction that opposes the change causing it — either the movement of the conductor or the change in the magnetic field. 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.
Quick Check: A student pushes a bar magnet into a coil, then holds the magnet still inside the coil. Explain what happens to the induced current while the magnet is still, and use Lenz's law to explain the direction of the induced current while the magnet was moving in.
While the magnet is stationary, no current is induced because the magnetic field through the coil is no longer changing. While the magnet was moving in, Lenz's law says the induced current flows in a direction that creates a magnetic field opposing the magnet's entry — so the coil pushes back against the incoming magnet, meaning the student has to do work to push it in. That work is what becomes the electrical energy.
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 18 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 9 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Electromagnetic Induction
What is electromagnetic induction?
Explain how a potential difference (voltage) is induced in a conductor in a magnetic field.