Lab Assignment: Magnetic Torque

In this lab you will explore the interaction of spinning magnets with magnetic and gravitational fields. Specifically the student will measure the value of the magnetic moment of a magnetized disk at the center of the snooker ball. The measurements will be performed in three different way each with its own set of errors. Some of the errors are correlated (related) some are not (uncorrelated) and the student will combine all three measurements into a single final result that properly handles the errors.

Assignment: 1 Measure the magnetic moment of the disk

The goal here is measure the magnetic moment of the magnetized disk at the center of the snooker ball. Instructions on how to perform the measurements are available from the teachspin website http://www.teachspin.com/magnetic-torque (especially this doc.)

1. First measure the magnetic moment via the gravitational torque method. The torque exerted by the gravitational field on a rod with a sliding weight is compared to the magnetic torque due to the disk inside the ball. Plot your data, with error bars, and then fit to a straight line. Determine the slope of the line and its error from the fit. Use the slope to determine the magnetic moment and its uncertainty. How is this better than just averaging the results?
2. Use the harmonic oscillation of the magnetized ball/disk system to determine the magnetic moment. Again fit your data to a straight line.
3. Use the precessional motion of the spinning magnetized/ball disk system to determine the magnetic moment. Make sure you understand how this method works. It may be helpful to go back to your physics 1 text book to review how the dynamics of rotational systems work in the context of angular moment conservation. With this you'll final understand why you don't fall off a bicycle when its rolling.
4. In all of the measurements above determine your errors carefully, both systematic and statistical (if you take repeated measurements) and include these in your results for each method.

Assignment: 2 Combine all three measurements

Combine all three measurements into a single final results that properly includes errors from the various systematic estimates.

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