16.1 - MAGNETISM Flashcards
What are lodestones? What are permanent magnets?
Lodestones are a magnetic material. They become magnetised. The poles of magnets attract or repel each other. Permanent magnets like compass needles have constant magnetic field.
What are magnetic fields shown by?
Magnetic fields are represented by lines of flux which pass from North to South.
Magnetic flux density is the strength of the magnetic field, determined by line spacing, denoted by B, and also known as the B field.
What are solenoids and how do they resolve the issue of where field lines point?
Solenoids are current carrying coils which result in a uniform B-field inside the magnetic.
What do flux lines tend to do?
Flux lines tend to straighten and shorten.
What is flux?
Flux is shown by a circle with a line cutting the middle. Flux = flux density * area. (in Wb, weber)
What is Faraday’s law?
Faraday’s law shows magnetic fields are caused by electrical currents, but that moving a magnet near wire can cause the magnetic flux of the circuit to change, inducing emf and so a current.
EMF is proportional to change in flux/change in time
What’s flux linkage and how does it change the emf equation?
In EM circuits, coils with several terms are used. The coil is usually part of a separate electrical circuit where emf is induced.
Flux linkage = number of coils * flux through one.
Emf = change in flux linkage / change in time
What’s Lenz’ law?
Induced emf induces current in a coil, meaning that it acts as a solenoid, inducing a magnetic field. If the induced current creates flux in the same direction, the change in flux causes a change in emf, increasing current and power dissipation. Therefore, the current will produce its own flux in an opposite direction, reducing the increase in flux. (Lenz’ Law).
Induced emf = -(rate of change of flux linkage)
