Electro/magnetic relationFebruary 27 2011 at 2:47 PM
Vince (Login MoxiFox)
Response to Light and travel analogy
I think this might be a confusing concept to people -it was to me, anyway. I still don't comprehend the why's fully, either.
Electricity and magnetism always go together like two links of a chain. Their "currents" go around in two circles like the links go around in two loops of a chain ... at right angles to each other. Each loop goes through the other loop but always at right angles ... exactly like 2 links of a chain go through each other.
When electricity flows in one direction only, it creates a magnetic "field" around itself with the magnetic gauss current flowing in a single direction as well. So ... you can make an electromagnet quite easily by wrapping insulated wire around an iron core (like a bolt or screwdriver) ... pass DC current through the wire and the iron will become a magnet with gauss flowing in one direction continually. (The gauss flows from the north pole through the air and back to the south pole in a circle or loop. Since air is a very poor gauss conductor, the gauss flow will be quite weak though. We experience this weak gauss flow through air from the North magnetic pole of the earth back across the earth's surface and down to the south magnetic pole. Over the top of the poles, a compass would point downward into the ground).
So it's very easy to create a steady-state magnet with a steady-state DC electric current.
The REVERSE doesn't seem to be true though. A magnetic flow occurs continually with a permanent magnet -such as you find on a stereo speaker- but ... there is no DC electric current flowing anywhere because of that speaker sitting in its location, dormant.
When you MOVE a magnet though, you DO create an electric potential! So in order to create an electric current with a magnet, the magnet must always be moving, changing speed and changing (reversing) directions continually. This will create spikes of electric potential (voltage) ... make a current if there is a conductor in the electrical loop ... and generate AC electricity if the magnet keeps changing speed smoothly and alternating directions at a fixed rate. (This is like the piston of an engine going up and down: it continually reverses direction and continuously changes velocity as well. The result is a nice smooth "sine wave" generation).
We generally associate AC current/voltage as coming from a transformer or alternator and calculate on the basis of sine waves ... but ... output voltage from a transformer isn't always necessarily in a sine wave formation! If you have a transformer with a turns ratio of -say- 1:10 and you put a smooth sine wave voltage of 5 volts on the primary side, you can expect the voltage output on the secondary side to be 50 volts AC. HOWEVER .... if you just apply 5 volts from a battery to the primary side, you'll see a huge spike of voltage develop on the secondary side -the voltage output depending on how fast you "snap" the primary battery! And ... when you RELEASE the connection, you'll see the opposite happen ... where a huge spike of voltage AGAIN appears on the secondary side .... and on the primary side too! (This is how engine "coils" work. Current is held steady through the primary winding, which results in no output on the secondary and then ... the connection is rapidly broken ... resulting in a voltage spike of many thousands of volts on the secondary ... creating the spark which jumps across the gap of the spark plug).
Since light is constantly fluctuating, the two components -electric and magnetic- are always present. So they're called "electromagnetic" radiation.