Magnetism Demo 2:  Field from a current-carrying wire.
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	Equipment:
		Lodestar DC Power supply (16V, 10A)
		large compass needle with stand
		mounted single wire with swiveling compass axis
		helmholz coils
		PS leads (black and red, banana + aligator)

	Demo 1:  Field from a single wire:

	Clip the leads to the two sides of the mounted wire (near the
base) and connect them to the power supply.  Balance the compass needle
on the swiveling axis. Turn the current control all the way down, and
the voltage control all the way up.  Set the range switch to
"High". Turn on the supply and turn up the current until it reaches 10
A.  Move the compass axis around to show the direction of the magnetic
field in different places.  The Earth's field is still comparable to the
field of the wire, so you will see the sum of the two contributions.
Reverse the leads, and show that the direction is reversed.  Once you
have the current level set, you can switch the supply on and off to
quickly see the effect of the current.

	Applications:  It is hard to do much with a single wire.  Even
with a large current, you don't get much of a field.  Thus...


	Demo 2:   Field from a coil:

	Clip the black lead to one of the "field" terminals of the
Helmholz Coils and the red lead to the other.  But the black compass
stand in the middle of the coils and balance the compass needle on
it. Turn on the supply, and raise the voltage to 16V with the current
limit turned up.  You should get about 4A.  This should have a dramatic
effect on the compass needle.  You can move the needle around and map
out the direction of the field.  You can reverse the current and show
that the field direction reverses everywhere.  Make the point that the
thing that counts is the product of the current times the number of
wires.  This coil has 260 turns total, so it has more than 1000
amp-turns compared to 10 amp-turns for the single wire in demo 1.

	Applications:  Virtually all modern electomagnets use coils:
soleniod actuators, MRI chambers,...