The Law of Conservation in Magnetism
Lenz's Law, named after Russian physicist Heinrich Lenz, is the companion to Faraday's Law. While Faraday tells us how much voltage is induced, Lenz tells us the direction of the induced current.
It states that the direction of an induced current is always such that it creates a magnetic field that opposes the change that produced it. This is essentially the electrical version of Newton's Third Law (Action and Reaction).
Understanding the Opposition
- If you move a North pole toward a coil: The coil will induce a current that creates its own North pole to push back against the magnet.
- If you pull the North pole away: The coil will induce a current that creates a South pole to pull it back.
In both cases, the coil fights against whatever you are trying to do. This ensures that energy is conserved; you must perform mechanical work to generate electrical energy.
The Formula (Conceptual)
Where:
=
Induced EMFN=
Number of turns=
Rate of change of magnetic flux-=
The negative sign represents Lenz's Law (opposition)Example Application
Imagine a metal ring falling through a magnetic field.
- As it enters the field, flux increases.
- Lenz's law says the ring will induce a current to push back.
- This magnetic "push back" creates a braking force that slows the ring down. This is the principle behind Eddy Current Braking used in roller coasters and high-speed trains.