Faraday’s Law of Electromagnetic induction is the process in which an electromotive force (emf) is induced in a closed circuit due to changes in the magnetic field around the circuit.
Lenz’s law states that the direction of the induced e.m.f. and hence the induced current in a closed circuit is always such as to oppose the change in magnetic flux producing it.
From the figure above:
- No. 1: The north pole of a magnet is moved towards the coil. By Lenz’ law, the coil will generate an e.m.f. such that a north pole is induced on the right side of the coil to oppose the change. (Why north pole? To “repel” away the incoming north pole) From the right hand grip rule, the current flow is as shown in the diagram.
- No. 2: The north pole is moved away from the coil. By Lenz’ law, the coil will generate an e.m.f. such that a south pole is induced on the right side of the coil to oppose the change.
- No. 3: The south pole is moved away from the coil. (Line of reasoning similar to above. Drop a comment if you have problems.)
- No. 4: The south pole is moved towards the coil. (Line of reasoning similar to above. Drop a comment if you have problems.)
From this, we can conclude that emf is induced whenever the magnetic field lines are “cut” by the coil. (A more proper terminology will be the change of magnetic flux in the coil induces an emf in the coil)
You might say that there are electrical energy generated from thin air as shown in the experiments. But there are no free lunches in the world (universe in this case). Mechanical energy (from pushing/pulling of the magnet) is converted into electrical energy. This is how cycling a bike with a dynamo converts your mechanical energy into electrical energy.
Fleming’s right hand rule:
Using Fleming’s right hand rule, you can predict the direction of the induced current with the knowledge of direction of magnetic field and force.