Hands-on Activity: Visualizing Magnetic Field Lines

Contributed by: VU Bioengineering RET Program, School of Engineering, Vanderbilt University

A comedic representation of a magnetic field shows a horseshoe-shaped magnet in a green field with lightning bolts emerging from each magnet end.
What exactly is a magnetic field?
copyright
Copyright © 2004 Microsoft Corporation, One Microsoft Way, Redmond, WA 98052-6399 USA. All rights reserved.

Summary

Students take the concept of etch-a-sketch a step further. Using iron filings, they begin visualizing magnetic field lines. To do so, they use a compass to read the direction of the magnet's magnetic field. Then, as they rotate the filings about the magnet, they observe the behavior of iron filings near the magnet. Finally, students study the behavior of iron filings suspended in mineral oil, which displays the magnetic field in three dimensions.

Engineering Connection

MRI machines produce very strong magnetic fields that must be carefully managed in order to protect personnel and patients from excessive polarization as the protons in their bodies align with the polar field. Patients may also possess implants or foreign objects that could interact with the magnetic field. Post-activity assessment questions 4 and 5 focus on the implications of a magnetic field as strong as that of an MRI, while question 6 focuses on those implications with respect to foreign bodies.

Learning Objectives

After this activity, students should be able to:

  • Describe the strength and direction of the magnetic field around a permanent magnet.
  • Predict and sketch magnetic field lines.

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Materials List

Each group needs:

  • compass
  • rubber-coated NdFeB magnet
  • paper holder for iron filings
  • 1 teaspoon of iron filings
  • clear bottle of prepared mineral oil*
  • 1 sheet of paper, 8.5 x 11 inches (20.32 x 27.94 cm)
  • masking tape

* Remove labels on a clear plastic bottle of mineral oil. Cut ~1 teaspoon of fine-grade steel wool into small shards. Put the steel wool shards into the bottle and recap. After shaking, the bottle displays magnetic fields in three dimensions.

Introduction/Motivation

In order to solve the grand challenge problem on MRI safety (presented in the associated unit), we need to understand the properties of magnetic fields.

While most introductory problems involving magnetism start with a uniform field, the only approximately uniform magnetic field that you experience in the lab is the magnetic field of the Earth. The magnetic fields of permanent magnets have very interesting shapes and directions. In this activity, you will be using a variety of methods to help visualize the shape of a magnetic field around various permanent magnets.

Procedure

Before the Activity

Gather materials and prepare the mineral oil bottles.

With the Students

  1. Present the Introduction/Motivation content to the class.
  2. Divide the class into groups of two to four students each. Hand out the materials.
  3. Direct students in the following experimental steps.
  4. Tape the magnet to the paper on its side, and place the compass somewhere on the paper. The compass points in the direction of the magnetic field. Make an arrow on the paper to mark the direction. Move the compass to a new position and repeat. Continue until you have marked the direction of the field over most of the paper. Warning: Do not bring the compass extremely close to the magnet or touch the magnet, which may remagnetize the compass to point in the wrong direction.
  5. Now remove the magnet from the page, place the iron filings in the paper container, and hold the magnet under the container. Watch the iron filings line up along the field. Hold the magnet in different orientations and observe the results.
  6. Shake the bottle of mineral oil and hold the magnet next to it. Observe how the suspended filings line up along the field. Change the orientation of the magnet to observe different points in the field.
  7. Conclude by administering the post-activity assessment, in which student individually write answers to six questions, as described in the Assessment section.

Assessment

Post-Activity Assessment

Journaling: At activity end, have students individually write answers to the following questions. Review their answers to assess their depth of comprehension.

  1. What does the map of the magnetic field you created with the compass remind you of?
  2. What do the iron filings look like in relation to the magnetic field you drew?
  3. What is different about the suspended iron filings and the iron filings on paper?
  4. Where does the magnetic field appear to be the strongest?
  5. How might this activity help us understand the much larger MRI magnet?
  6. What types of things would be safe in a larger magnetic field and what would be unsafe in a larger field?

Contributors

Eric Appelt

Copyright

© 2013 by Regents of the University of Colorado; original © 2006 Vanderbilt University

Supporting Program

VU Bioengineering RET Program, School of Engineering, Vanderbilt University

Acknowledgements

The contents of this digital library curriculum were developed under National Science Foundation RET grant nos. 0338092 and 0742871. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: June 16, 2017

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