Background
A magnet is a material with poles and a magnetic field created by the configuration of its electrons. Magnets can attract and repel because of the magnetic fields around the magnet. All magnets have magnetic fields around them, and it is this magnetic field, and the poles of the magnet, that are defining characteristics of all magnets. They are essential parts of many devices that we use on a daily basis, including: cars, televisions, radios, and computers. There are two groups of magnets. Permanent magnets are magnets with permanent magnetic fields. They cannot be turned off, nor can their fields be increased or decreased easily. These are items that are almost always magnetized. To remove a magnetic field from a permanent magnet requires increasing the temperature of the magnet. This adds heat and energy to the system and any magnetic fields that were present disappear. The temperature at which the magnet no longer holds its field is known as the Curie point. The other group is called temporary magnets. This category includes items that are magnetic, but do not contain their own magnetic fields. Items in this group include paper clips, scissors, iron rods, staples, and various other items. These must be made out of one of the three metals that are naturally magnetic. They are iron, nickel, and cobalt. If something attracts to their magnets, it must have one of these metals in it.
Why do this in your classroom?
- To encourage the following process skills for scientific investigation: prediction, observation, developing a hypothesis, and drawing conclusions.
- To help students understand magnets and what creates magnetism.
- To allow students to manipulate materials and explore their own questions.
Materials
- Various permanent magnets of different shapes, sizes, and strengths. These can be purchased from toy stores and hardware stores, as well as online.
- Paper clips
- Magnetic items
- Metal non-magnetic items
Procedure
- Using a simple colored bar magnet, show the powers of attraction by bringing like poles together. Next place the opposite poles together to show the repulsion. Point out that all magnets have two sides — a north pole and a south pole. Tell the students that a four word phrase highlights the basic science of magnets: “opposites attract, likes repel.”
- Show the students a paperclip, and ask them if this is a magnet. Then ask if the paperclip is magnetic. The paperclip is a temporary magnet. Ask the class if they can think of temporary magnets they may have in their home. Some answers include their refrigerator doors, car doors, the metal legs of their chairs and desks.
- Attach the paperclip to the magnet, and ask the class if you can attach another paperclip to the first one. Since the paperclip has been magnetized, it can attract another paperclip. Ask the students what will happen if you remove the top paperclip (and the one below it) from the magnet. Gently pull the top paperclip, and both of them should still attract to each other. If you’re very gentle, you can even separate the two paperclips and bring them back together. They still attract! But if you drop them on the table, their field will be lost.
- Pass out the magnets, and challenge the students to discover something new about magnets. Tell them it can be anything, something interesting or curious as long as it is new to them. During the exploration they can utilize objects in the classroom like tables, chairs, and other school supplies to test what is magnetic and what isn’t.
- Ask a few students to share with the class what they have learned, and have the other students repeat the demonstration using their own magnets. Can they figure out which magnet has the largest field? The strongest field?
What’s happening?
When it comes to the creation of magnetic fields, the spin of a material’s unpaired electrons is the crucial element. In most materials, electrons spin randomly. But in magnets the electrons group into magnetic domains, created whenever the spin of a number of electrons line up in the same direction. This happens in iron, nickel, or cobalt. If a majority of magnetic domains match spins, then that material is said to be magnetic. That material then has a north pole, a south pole, and a magnetic field, each determined by the directions of the spins. These domains support each other by pulling more in the same direction, resulting in an overall magnetic field.
For more information contact MagLab educator Carlos R. Villa.
