Magnetic Fields 2 Flashcards
Define Magnetic Flux Φ
The product of magnetic flux density (B) and the given area (A) when the field is perpendicular to the area
Can be seen as just the number of field lines (If the system was to be shown on a diagram)
What is Magnetic Flux Linkage
NΦ
The magnetic flux multiplied by the number of turns N, of a coil
Basically a measure of how much flux lines connect/interact with the coil
So the more coils or the more field lines, the more ‘connections’ there will be between coils and field lines in the system, the higher the flux linkage
If the field lines are parallel to the coil, there will be no connections
Unit of Magnetic Flux Linkage
Wb
Weibers
Explain how electromagnetic induction is caused
When a conducting rod moves relative to a magnetic field, the electrons in the rod will experience a force (as they are charged particles), and build up on one side of the rod, causing an emf to be induced in the rod
Or if you move a bar magnet relative to a coil of wire
What is Faraday’s Law
The magnitude of induced emf is equal to the rate of change of flux linkage
What is Lenz’s law
The direction of induced current is such as to oppose the motion causing it
How could one show Lenz’s law
Measure the speed of a magnet falling through a coil of wire, and its speed when falling from the same height without falling through the coil.
What you will find is that the magnet takes longer to reach the ground when it moves through the coil
Explain, using Lenz’s law, the experiment to show Lenz’s law
- As the magnet approaches the coil, there is a change of flux linkage through the coil so an emf and a current is induced (By Faraday’s Law)
- Due to Lenz’s law, the direction of induced current is such as to oppose the motion of the magnet so the same pole as the pole of the magnet approaching the coil will be induced in order to repel the magnet.
- This causes the magnet to slow down, due to electrostatic forces of repulsion.
