Question 12: Use your observations to this point to respond to each of the following

student predictions of the best way to produce a uniform magnetic field for use in mass spectrometry. Be sure to indicate with which student, if any, you agree, and explain why.

1. We predict that two closely spaced (nearly touching) coils with current flowing in

opposite directions will produce the most uniform magnetic field. The region of

interest is on opposite sides of the two coils, and therefore opposite current flow is

needed for the fields to point in the same direction. Keeping the coils close together

means we benefit from the region of strongest field of each.

2. We predict that two closely spaced (nearly touching) coils with current flowing in

the same direction will produce the most uniform magnetic field. This is because the

continuous field lines "looping" through both coils will be in the same direction. We

agree with the claims Prediction 1 makes about coil spacing.

3. We predict that two coils placed far apart (far larger than the radius of the coil) with

current flowing in the same direction will produce the most uniform magnetic field.

We saw experimentally that the edge around each coil is where uniformity breaks

down; we conclude that we should move the coils far apart and have the uniform

region away from these edge effects.