May 12th - Magnets

Class started with the students discussing what they already know about magnets. We also went over the idea that magnets can attract or repel each other, just like electrical charges and the subatomic particles. In magnets, opposite poles (North and South) attract while like poles repel.

Close Encounters Lab – Each student was given two balloons, a marker, and some string. The students blew up each balloon then tied a piece of string to the end of each one. They labeled one balloon “A” and the other “B.” The free ends of each string was then taped in an open door frame.

The students charged Balloon A first and then observed the balloons. They then charged both balloons and observed.

We got really good results with the two charged balloons and were able to see them repel each other. We really didn’t see Balloon A attract Balloon B in the first part of the experiment but the students did understand this was supposed to happen.

Fun Fact – Magnets got their name from the region of Magnesia, which is now part of modern-day Greece. The first naturally occurring magnetic rocks, or lodestones, were found in that area almost 3,000 years ago. A lodestone is composed of an iron-based material called magnetite.

Iron from Cereal Lab – Prior to starting this lab we spent a few minutes discussing iron in foods. I asked the students if they knew reasons why humans need to consume iron and we spoke a little about the functions of iron and sources of iron.

Iron primarily functions as an oxygen carrier in the blood. It also assists with the immune system, cognitive development, temperature regulation, and energy metabolism.

Each student had a bowl of Corn Flakes that we added water to. We started out using a fork to make the cereal mushy but decided a blender would do a better job. Once the cereal was soggy, the students stirred a magnet through the cereal and then wiped it on a paper towel. We were able to find some small amounts of iron (it looks like black fuzz).

A few weeks ago, we went over Coulomb’s Law. This law states that the attraction or repulsion of two electrical forces becomes greater as the two charged objects get closer together. This same effect can be demonstrated with magnets. We used two bar magnets and found that as they were moved closer together, the attraction or repulsion became stronger.

Magnetic Domains – Magnetic materials contain magnetic domains. These are clusters of atoms that behave like tiny magnets. Objects are not magnetic when the magnetic domains are randomly arranged. However, if they do all line up, the object takes on magnetic properties. This explains how a nail or paper clip can become magnetized.

Permanent and Temporary Magnets – Some metals are permanent magnets due to the fact that their magnetic domains are permanently lined up. Fridge magnets and the magnets we had in class (horseshoe magnets, bar magnets, ring magnets) are all examples of permanent magnets.

Temporary magnets are metals that can be made into a magnet by lining up the magnetic domains. These include iron and nickel. Rubbing a paper clip or nail on a magnet will cause the magnetic domains to line up, creating a temporary magnet. An electromagnet is another example of a temporary magnet.

Suspended Airplane Lab – The students each created a small “wing” by folding up a piece of crepe paper. They inserted a pin through the center of the paper wing and then tied a piece of sewing thread to the head of the pin.

Each student placed a bar magnet on the edge of the table and then held the wing out in front of the magnet. The students observed as the wing was attracted to the magnet.

The magnetic field surrounding the magnet exerted the attracting force on the pin/wing. The pin and magnet both have magnetic properties. The two objects pulled on each other with enough force to overcome gravity, allowing the wing to remain suspended in the air.

Compasses and Earth’s Magnetic Field – The students all know Earth has a North Pole and South Pole. We are able to use compasses because the Earth acts like a giant bar magnet. The needle of the compass aligns with Earth’s magnetic field. The needle will point in a direction that lies along the magnetic field line at that point.

An interesting fact about Earth’s poles: Earth’s North Pole is actually at the south end of its magnetic field while its South Pole is at the north end of its magnetic field.

Swinger Lab – Each student was given a compass, a piece of sewing thread, a small paper clip, a ruler, some tape, a heavy book, and a magnet. They taped one end of the thread to the paper clip and then taped the other end to the ruler. The students then placed the ruler inside the book and placed the book on the edge of the table. They magnetized the paper clip by holding it on the bar magnet for several seconds. The students removed the paper clip from the magnet then let the clip swing freely. The compasses were placed on the table next to the book and the students observed the movement of the compass needle and where it stopped. The compasses showed that the paper clip pointed North-South once it stopped swinging.

The north poles of all magnets are attracted to the Earth’s north magnetic pole. Magnets are all north-seeking poles. As long as the paper clip is magnetized (its magnetic domains are lined up in a north-south direction), one end will point toward Earth’s magnetic north pole.

Electromagnet Lab – We attempted to make electromagnets using both insulated wire and bare copper wire. We didn’t have any luck with the insulated wire and only one student was able to get the electromagnet with the copper wire to work.

For this, the students wrapped the wire around a nail. They attached the free ends of the wire to a D-cell battery in a battery holder (one end to each battery terminal). They then tried to use the electromagnet to attract paper clips.

The Direct Current running through the battery should have caused the magnetic domains within the nail to line up causing it to become magnetic.

This is an easy one to try at home. Experiment with different types of wire or different nails. You can use electrical tape to attach the wires to the battery terminals.

Uses of electromagnets – Electromagnets are used in motors, CDs, computer hard drives, and alarms. I showed the class a transparency with a diagram of an alarm bell and asked them to locate the electromagnet. We also discussed how the electromagnet causes the alarm’s hammer to vibrate and create the alarm’s sound.

We finished up class by using magnets to move iron filings. The iron filings were attracted to the magnet that was moved over or under the plate the filings were on. The students were able to make patterns and also observed the filings “jump” up to stick onto the magnets. The filings are pulled toward the magnet when they enter the magnet’s magnetic field.

Next week:

Next week will be our last class session for the year. We'll study balance and flight. The students will review center of gravity (a topic we covered back at the beginning of the school year). We'll also learn about lift, thrust, and drag and how these forces, along with gravity, affect planes. 

References:

The labs "Close Encounters," "Swinger," and "Suspended Airplane" are all from Physics for Every Kid.

VanCleave, J. (1991). Physics for Every Kid: 101 Easy Experiments in Motion, Heat, Light, Machines, and Sound. San Francisco: Jossey-Bass.

I found the "Iron from Breakfast Cereal" lab on this website: http://chemistry.about.com/cs/howtos/ht/ironfromcereal.htm

The idea to make electromagnets came from a Lakeshore Learning Materials kit on Electricity.