Notice that when we studied gravitational fields we concentrated on forces acting on masses and when we studied electrical fields we concentrated on forces acting on charges. You would expect that when we study magnetic fields we would concentrate on forces acting on magnets. Not so......Instead we will be studying other things. Why?....Well because there is a relationship between magnetism and electricity that if we study will provide a deep insight into physics. Historically many scientist contributed to the explanation of this relationship. Maxwell summarized the relationship in 4 equations known as ........
Maxwell's Equations - (note: these are greatly simplified and the equation is not shown)
Simplified Description of Equation |
AKA |
Crutial Experiment |
What We Need to Know for IB |
|
1 |
Electrical Charges produce Electric Fields |
Gauss's Law for Electricity |
Like charges repell and unlike charges attract proportional to inverse square of their separation. A charge on an insulated conductor moves on its outer surface.
|
already covered (electric fields) |
2 |
There are no Magnetic Monopoles |
Gauss's Law for Magnetism |
It has not been possible to date to verify the existence
of a magnetic monopole. |
magnets always have a north and south pole Magnetic field lines are continuous and do not have a beginning or end whereas electric field lines begin and end on electric charges. |
3 |
A changing Magnetic Field causes an Electric Field |
Faradays Law of Induction |
A magnet thrust through a closed coil of wire will
set up a current in the loop. |
A conductor moving in a magnetic field will produce
an EMF |
4 |
A changing Electric Field causes an Magnetic Field |
Amperes Law (modified by Maxwell) |
A current in a wire sets up a magnetic field near
the wire. |
Electric Currents in a wire or a coil cause a magnetic
field. |
We also need to know that like poles repel and unlike poles attract.
It is possible to investigate these relationships farther to show how optics and the speed of light is related to these equations (the speed of light can be calculated from purely electromagnetic measurements) and how these equations have an intimate link with Einstein's Special Relativity Theory.