It is an inductor. It generates a magnetic field in response to a current. Energy stored is L*I*I/2. It will have some series resistance due to the windings, but primarily inductance. V = L*di/dt = N*dPHI/dt. So inductance and flux are directly related. Flux is your measure of guass.
Hello again moffy and dougy,
moffy:
QUOTE: "Flux is your measure of Gauss"
Sorry but no, it's flux *density*. And the flux *density* is much higher in the steel than in the air. In the steel it is confined, in the air it spreads out. That's why the steel can do so much good and the air does so much harm.
But as long as you want to relate this to an inductor, you cant tell me that if you take an air core coil and measure the inductance with an without a 5000u core that the inductance isnt going to go up significantly, even if it is a straight coil that does not curve back to meet the other end.
moffy and dougy:
There's not much room for argument as i have direct experience with this in actual applications that measure the field strength. So i know for a fact that when you add steel you get a higher concentration of flux which in turn results in higher field strength near the ends of the steel. Without the steel the measurement may even be too low to be useful, but with the steel the measurement picks up significantly enough to be measured in a given application.
Also, you two must still be looking at the properties of a finished inductor. In a normal inductor with an air gap, the air gap reduces the total inductance measured across the leads electrically, but that measurement does not reflect what is happening inside the steel. The steel acts as a sort of 'lens' that concentrates the flux into a much smaller cross sectional area than can be possible in the air. So the flux is the same, but the flux density is much greater in the steel. So the air does in fact affect the *overall* inductance to a great extent, but it does not modify the actual properties of the steel itself in that you'll still see a higher measurement of Gausses at the end of the coil with the steel than without.
But you dont have to take my word for it, so a simple experiment. Get a linear hall effect device and wind a straight cylinder coil. Apply an appropriate current. Measure the field strength at one end of the coil using the hall device. Next, insert a 10 penny nail inside the coil, then repeat the measurement. Note how much it went up. For best results find some 20kG steel and try that and see how MUCH more it went up.
You can also measure the inductance if you like, but you'll have to watch the frequency and match it to the steel and it might not work too well with the nail depending on how much current you use.
Also one more small note:
We are still in the information gathering phase here anyway. What this is starting to look like is the magnet face will be one side of the 3 meter length. That means the front face will be 5cm x 3 meters, so the distance from the front of the magnet to the back of the magnet may only be 5cm.
Another quick question for the OP:
Have you tried rare earth magnets yet?