Physics / core

Lenz's Law

Also known as: Lenz's rule

definition

The direction of an induced current is always such that it opposes the change in magnetic flux that produced it. Lenz's law determines the direction of induced currents and explains regenerative braking in electric vehicles, eddy-current brakes in trains, and the damping behaviour of electromagnetic systems.

💡 Intuition

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

Core Idea

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

Formal View

Lenz's law is encoded in the negative sign of Faraday's law: \mathcal{E} = -\frac{d\Phi_B}{dt}. The induced EMF drives a current whose own magnetic flux opposes the change in the external flux \Phi_B, ensuring conservation of energy.

🔬 Example

Drop a magnet through a copper tube — it falls slowly because the induced currents create opposing magnetic fields that brake the magnet.

🎯 Why It Matters

Lenz's law determines the direction of induced currents and explains regenerative braking in electric vehicles, eddy-current brakes in trains, and the damping behaviour of electromagnetic systems.

⚠️ Common Confusion

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

💭 Hint When Stuck

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.

Related Concepts

Next Steps

generator

How Lenz's Law Connects to Other Ideas

To understand lenz's law, you should first be comfortable with faradays law and electromagnetic induction. Once you have a solid grasp of lenz's law, you can move on to generator.

Go Deeper

Worked Examples

Step-by-step solved problems

Practice Problems

Test your understanding

Frequently Asked Questions

What is Lenz's Law in Physics?

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

Why is Lenz's Law important?

Lenz's law determines the direction of induced currents and explains regenerative braking in electric vehicles, eddy-current brakes in trains, and the damping behaviour of electromagnetic systems.

What do students usually get wrong about Lenz's Law?

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

What should I learn before Lenz's Law?

Before studying Lenz's Law, you should understand: faradays law, electromagnetic induction.