Understand that a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an electromotive force (e.m.f.) in the conductor.
When a conductor (like a wire) moves through a magnetic field, or when the magnetic field around a conductor changes, an electric current is produced. This is called electromagnetic induction.
Think of a magnet as a “magnetic wind.” When a conductor cuts through this wind, it feels a force that pushes the electrons in the wire, creating a flow of charge – an e.m.f. The faster the conductor moves or the faster the field changes, the stronger the e.m.f.
The induced e.m.f. is given by Faraday’s law:
\$\mathcal{E} = -N \frac{d\Phi}{dt}\$
Where:
Magnetic flux is the amount of magnetic field passing through a given area:
\$\Phi = B \, A \, \cos\theta\$
Where:
Imagine a roller coaster (the conductor) moving through a tunnel filled with invisible magnetic “winds.” As the coaster speeds up or slows down, the wind pushes against the cars, causing them to move. The faster the change, the stronger the push – just like a faster change in magnetic flux creates a stronger e.m.f.
The negative sign in Faraday’s law tells us that the induced e.m.f. always opposes the change that produced it. This is known as Lenz’s law.
| Scenario | Direction of Induced Current |
|---|---|
| Coil in a growing magnetic field (field increasing into the page) | Counter‑clockwise (to create a field out of the page) |
| Coil in a decreasing magnetic field (field decreasing into the page) | Clockwise (to maintain the field into the page) |