Lenz's Law Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Lenz's Law.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

The direction of an induced current is always such that it opposes the change in magnetic flux that produced it.

Nature resists change — when you push a magnet into a coil, the coil creates its own magnetic field that pushes back.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Lenz's law is the magnetic version of 'every action has a reaction' — it ensures energy conservation in induction.

Common stuck point: Lenz's law is about the direction of the induced current, not its magnitude (that's Faraday's law).

Sense of Study hint: When applying Lenz's law, first determine whether the magnetic flux through the loop is increasing or decreasing. Then the induced current must flow in the direction that creates a magnetic field opposing that change. Use the right-hand rule to find the current direction from the opposing field direction.

Worked Examples

Example 1

easy
A north pole of a magnet is pushed toward a coil. According to Lenz's law, what pole does the coil's nearest face become? In which direction does the induced current flow (viewed from the magnet's side)?

Solution

  1. 1
    Lenz's law states the induced current opposes the change that caused it.
  2. 2
    The approaching north pole increases the flux through the coil. To oppose this increase, the coil must create a magnetic field that repels the magnet.
  3. 3
    The nearest face of the coil becomes a north pole (repelling the incoming north pole), so the current flows counterclockwise when viewed from the magnet's side.

Answer

\text{Coil face becomes north pole; current flows counterclockwise (from magnet's view)}
Lenz's law is a consequence of energy conservation. The induced current always creates effects that oppose the change in flux, requiring work to be done to maintain the change.

Example 2

medium
A circular loop is in a magnetic field pointing into the page. The field strength decreases. According to Lenz's law, in which direction does the induced current flow?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
A conducting ring is dropped through a region of magnetic field. As it enters the field, the induced current creates an upward force on the ring. Explain this using Lenz's law.

Example 2

hard
A superconducting ring (zero resistance) is in a magnetic field of 0.5 \text{ T}. The external field is suddenly turned off. What happens to the flux through the ring, and why?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

faradays lawelectromagnetic induction