Lenz's law
As a magnet approaches a coil, the coil "pushes" it away.
When the magnetic flux through a coil changes, an induced current flows in the coil, and the magnetic field of that current always opposes the change in flux. As the magnet approaches, a like pole appears at the near end of the coil and repels the magnet; as it moves away, an unlike pole appears and attracts it, summed up as "repel the approach, attract the retreat". The faster the magnet moves, the greater the rate of change of flux and the larger the induced emf.
Induced EMF vs. time
The closer and faster the magnet, the larger the emf; its sign reverses between approaching and receding.
Think about it
When the magnet's N pole approaches the coil, what pole forms at the end of the coil nearest the magnet?
An N pole. The induced current's field opposes the increase in flux, so an N pole, the same as the magnet's, appears at the near end, and the two repel each other.
Model assumptionsMagnet's field approximated by the on-axis dipole field · Coil and ammeter total resistance 10 Ω
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.