How many loops are necessary to create a solenoid with a uniform
magnetic field? Build a solenoid by adding current loops to
the simulation.
When you put the first coil down (or any later coils), you can move
it around .. and if you click-drag one of the ends, you can change the
radius of the coil ... watch how the field strengths change as you change
the coil size. (If you drag one end "across the x axis", you
will reverse the direction of the current in the coil (remember, for the
current directions, OUT=RED and
IN=BLUE).
You can measure the magnetic field by click-dragging the mouse and
observing the yellow message box.
You can also superimpose field lines by double-clicking inside the
animation.