Day 3: Mapping a Dipole Magnetic Field
Student Pages

Today we will use the magnetometer to make a map of a bar magnet's effect on the space around it. We will work in groups of two to collect observations and analyze the observations. We will discuss our work as a class.

Materials:

• Bar magnet.
• Three different color markers or pencils.
• 3-4 sheets of poster paper per group.
• Magnetometer as built in Day 2 Lesson.
• Tape.

Activity 1

Goal:
Obtain a good quality representation of the spatial region affected by the bar or dipole magnet.

Data Collection Procedure:

• Along the edges of the paper, mark points separated by 10cm and draw a grid on the paper.
• Place the paper on a lab desk. Use tape to mark the edges of the 4 corners so that you could place another paper in exactly the same position.
• Place bar magnet horizontally in center of paper. Tape magnet to paper. Outline the position of the bar magnet relative to the grid on the paper.
• Use the magnetometer to determine the direction of the magnetic field at each grid point.
• Record the direction of alignment by drawing a short directed line segment that accurately shows the direction the detector magnet is pointing at that location. The line segment should be centered on the point directly below the center of the magnetometer and should be about an inch long.
• Repeat at each grid intersection.
• Put a legend on the completed map which includes information about the orientation of the map relative to some fixed reference point in the room (a wall clock or a door for instance).
• Put a title on the map as follows: Bar Magnet Map, date, and your group identification

Data Analysis Questions to be Done by Small Group

• Are all the arrows pointing in the same direction? Explain why you think your data is correct or incorrect.
• Describe the geometric shape the arrows seem to indicate.
• Suppose I have a magnetometer and several other magnets. If I bring one magnet near the magnetometer, the magnetometer will deflect. If I bring two magnets near the magnetometer but at different locations, will I measure the combination of the effect of the two magnets or just the effect of one of them? Write a convincing argument for your opinion.
• While gathering data, did you record the effect of just the bar magnet or the bar magnet and some other things? Name the sources of all effects. Look closely at the lab table and vicinity for possible answers. Consider the materials you worked with the first day of the magnets unit for hints.
• Can you subtract or otherwise remove the unwanted effects to get the effect of just the bar magnet? Explain your answer.

Break for Class Discussion

Activity 2

Purpose:
Obtain representation of ambient or background magnetic effects at location of Activity 1.

Data Collection Procedure:

• Place a clean sheet of paper in the same location as in Activity 1. Draw a 10cm grid on it.
• Without any other magnets near by, place the magnetometer at each grid intersection and record the direction of its alignment with a 2nd color marker.
• Put a legend on the completed map which includes information about the orientation of the map relative to some fixed reference point in the room (a wall clock or a door for instance).
• Put this title on the map: Earth Magnet Map, date, and your group identification

Data Analysis Questions to be Done by Small Group

• Are all the arrows on the Earth Magnet Map pointing in the same direction? Explain why you think your data is correct or incorrect.
• Are any of the arrows pointing in the opposite direction, or approximately so, as adjacent arrows? Propose a reason for such variations.
• Under what conditions can the effect of a magnetic change?

Break for Further Discussion

Suggested Homework:
Read about the interaction between the solar wind and the earth's magnetic field.

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