Planet Magnet

Students use iron filings to explore the magnetic field around a magnet and record their observations. Next, students apply their experience with the magnet to understand the magnetic field around Earth. Following their investigation, students summarize their findings.

Learning Goals

  • Students will learn that dipole magnets have predictable and similar fields and that the magnetic field lines extend far beyond the magnet itself.
  • Students will learn that magnetic particles (like chips and fillings) are attracted to magnets and will orient to follow the magnetic field.
  • Students will develop an understanding of Earth’s magnetic field

Learning Objectives

  • Students will make and record observations of magnetic field lines around a dipole magnet.
  • Students will communicate scientific work and observations to peers.

Materials

For Student Teams

  • Shallow box or cafeteria tray
  • Bar magnet
  • Plastic bag
  • Tape
  • White paper
  • Magnetic chips (or iron fillings) in a salt shaker
  • A round piece of construction paper (see Preparation section below)
  • Compass

Bar magnet with iron fillings showing the magnetic field

Preparation

  • Note: Iron filings are traditionally used in this classic classroom activity, however, they can be messy in a classroom setting. Using "magnetic chips" (small pieces of zinc-plated iron wire) instead is less messy and their elongated shape makes it easier for students to see the field lines. 
  • Cut circles out of colored construction paper with a diameter that is about the same length as the bar magnets. (Alternatively, instruct students to do this during the activity.)
  • Prepare images of Earth's Dipole Magnetic Field and Earth's Magnetosphere to show to the class.

Directions

  1. Assign students to small groups. Explain that students will make and record observations of magnetic fields.
  2. Provide each group with supplies and allow students at least 15 minutes to make and record observations. Students should generate understanding of how the chips or fillings interact with a magnet. Understanding that the chips are magnetic is essential for understanding results of the second part of the experiment. Consider pausing after students have reached this stage and reviewing the result.
  3. Then, students should come to an understanding that the magnetic chips/filings align themselves to a magnetic field. Students should be able to see the shape of the field and describe this by drawing a picture. (Note: Students may use too many or too few chips/fillings to see the shape of the field. You may recommend that students repeat this part of the activity multiple times to ensure that the shape of the field they find is consistent each time. In science, this is called having multiple replicates or trials. Scientists do this to ensure validity of experimental results.)
  4. Show pictures of Earth’s magnetic field and magnetosphere and discuss how Earth behaves like a magnet. Ask students if the magnetic field they made looks like the field in the pictures. Have students place the planet shape at the center of their field and add the shape to their drawing.
  5. Ask students if they can tell the north end from the south end of their magnet. They will not be able to figure this out using only the fillings/chips. Have students use a compass to deduce the polarity of the magnet and label their drawings. If students are not familiar with how a compass works, provide a brief introduction to how to use it and how it reacts to Earth’s magnetic field.
  6. Clean up: Instruct student groups to move the magnet-filled bag around their tray to collect the chips/fillings (which will stick to the outside of the bag). Have students place their bag over a bowl and then open the bag and remove the magnet. The chips/filings should fall into bowl.

Summarizing and Reflecting

Time permitting, have student groups summarize their experiment by making a poster. Students should include information on their poster about (1) what they did/methods, (2) what happened/results, including a drawing of what the chips looked like when oriented over the magnet, (3) what they think it means/interpretation. Hang posters around the classroom and compare results of different groups.

Background

Magnetism is one of the main forces of nature. Like the force of gravity, which causes objects to be attracted to each other, magnetism causes magnetized objects to be attracted to each other. Simple dipole magnets have two poles: a "North" pole and a "South" pole. If two magnetic objects are brought together, the North pole of one will “stick” to the South pole of the other.

Earth's Dipole Magnetic Field

In this activity, the magnetic chips or filings align themselves along the lines of magnetic force. These lines of force point from the positive pole to the negative pole of the magnet. When students sprinkle magnetic chips onto their magnet they first learn that the chips are magnetic (because they “stick” to the magnet). They then explore how magnetism forces the chips to line up in the direction the magnetic force points, allowing them to see the shape of the magnetic field.

Earth is an example of a dipole magnet, where the lines of force point in a direction out of the South (magnetic) Pole and into the North (magnetic) Pole. The magnetic field is made by currents of molten material which move around deep within our planet. On Earth, a simple compass can always be used to detect the presence of the magnetic field of the Earth, as well as any other nearby magnetic fields such as magnetic metals (refrigerator doors, for example). The needle of the compass acts like the magnetic chips or filings used in this activity.

Extensions

  • This activity is a great way to introduce students to magnets and magnetic fields in a guided format and can be extended by allowing student groups to design their own experiments using magnets and/or magnetic chips in a true inquiry format. Have students develop a question about magnets, a related hypothesis, and experiment to test their hypothesis.
  • Have students collect their own iron filings by dragging a magnet through sand or dirt. Students may do this with a box of sand or outside in places such as dunes, the seashore, or a desert.