AQA GCSE Lenz's Law (Physics)
Lenz’s Law
Lenz’s Law says that when a magnetic field changes near a conductor, it creates a current that makes its own magnetic field and that new field tries to oppose the original change.
The original change is either the movement of the conductor or the change in magnetic field.
This sounds complicated, but its not that bad. Let us have a look at an example of the northa pole of magnet being pushed into a coil.
Example 1
In the diagram below, the north pole of a bar magnet is pushed into a coil of wire.
As the bar magnet goes into a coil of wire, the coil of wire will cut the field lines around the magnet. This will induce a potential difference across ends of coil, if a complete circuit is present, then a current will flow.
In this case, the current will be anticlockwise. Due to the current flowing through the coil, a magnetic field is created around the coil. The end of the coil that faces the magnet will become a north pole, the opposite end of the coil will become a south pole.
This will cause repulsion between the magnet and the coil of wire.
Example 2
In the diagram below, when the north pole of a bar magnet is pulled out of the coil, again a current flows in the coil, but this time it will be a clockwise current.
Due to the current flowing through the coil, a magnetic field will form around the coil, with the south pole of the coil, being near the north pole of the bar magnet. As a result the bar magnet will be attracted to the coil.
(The explanation for example 2 has been simplified as it was explained in example 1).
Summary table
Use the table below to help you work out the direction of current through the coil and also the induced magnetic pole of the coil.
| Pole of bar magnet going into or out of the coil | Enterning coil or leaving coil | Direction of current in the coil | Magnetic polarity induced in the coil near the bar magnet | Magnet and coil attracting or repelling |
|---|---|---|---|---|
| North | Entering | Anticlockwise | North | Repel |
| North | Leaving | Clockwise | South | Attract |
| South | Entering | Clockwise | South | Repel |
| North | Leaving | Anticlockwise | North | Attract |
Practice Question
1.State what Lenz’s law is
2. A south pole of a magnet is being pushed into a coil. Explain why the coil repels the magnet
3. If a south pole of a magnet is pulled out of a coil, will the current flow clockwise or anticlockwise through the coil?
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