Day 5: Interpreting Magnetic Field Maps
Lesson Plan

Activity Goals:

Students will be able to:
(a) Interpret magnetic field maps.
(b) Rotate the coordinates to obtain different views.
(c) Change the coordinate representation.
(d) Produce alternate graphical representations.

Materials:

• 2 bar magnets
• 4-6 ring magnets (large diameter if available)
• 2 cups
• Graph paper
• Magnetometers

Homework due:

Assigned homework was to draw the field lines for 5 different arrangements of pairs of dipole magnets. The essential features are that lines go between opposite poles, field lines always start on one pole and end on the other, field lines have definite direction, and field lines do not cross. Students will be asked to explain their predicted maps and differences from actual observations.

Activity 1

Ask students to test one of their homework predictions. If possible, have all 5 combinations tested by at least 2 groups. Ask each group to report out results, including how the earth's magnetic field has hampered the measurements. This could be used as a graded exercise as it requires application of the previous class activity and compares a prediction with an actual observation.

Activity 2

Students will map the field of a stack of ring magnets. First map the field of the stack while the stack is lying on its side, forming a tunnel, if you will. Second, map the stack on end, forming a well, if you will.

Questions: The same magnets produced each of the mapped fields. What is different? Are the two maps representations of the same thing? If so, how is the thing changed between representations? Where both of the representations present in each of the mapping exercises? Could you have turned something else on its side to get the two different maps?

Activity 3

Students will look at a map of the field near the end of a single dipole magnet. Students will make a plot of how the magnetic field would appear to a magnetic particle that was moving through the field perpendicular to the long axis of the bar magnet, but in the plane of the bar magnet as shown.

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|               |     |

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V

```

The desired graph will show magnetic field strength on the vertical axis and distance traveled on the horizontal axis. The expected graph is as follows.

Repeat the exercise but let the magnetic particle move in the plane of the magnet parallel to the long axis of the magnet. The same axis will be used but this time the field will show variation in sign and in strength.

```
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|               |

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The expected graph will resemble the following.

Homework suggestion:

Construct a way of making a magnetic field that had only straight field lines.

Lesson Development/Writing: Ed Eckel
Web Design: Theresa Valentine
Last Updated: 8/24/2000