Magnetism - Invisible Forces
When you researched about magnets, you probably learned something about magnetic fields. What are magnetic fields?
The area of a magnet's force is called a magnetic field.
Generally speaking, the larger the magnet, the stronger the magnetic force and the more area it covers. That means that objects containing iron will be attracted to a larger magnet from greater distances.
You can see the magnetic field of magnets by placing iron filings around them.
You're the scientist!
You may have seen the effects of a magnetic field, but you cannot see a magnetic field. This is because a magnetic field is not made of matter. It is made of magnetic energy. By putting something into a magnetic field that is attracted by it, you can see where it is.
CAUTION: Do not do this activity anywhere near your computer! Some of the ingredients in the activity could be very harmful if they got in your computer or its keyboard!
- Two magnets (you might try bar magnets, disk magnets, or horseshoe magnets)
- Iron filings
- Three sheets of heavy paper
- Spray paint or spray lacquer (optional)
- Place a bar magnet on the table. Put the other magnet far enough away so that its magnetic field cannot affect what you are doing.
- Put the sheet of heavy paper on top of the magnet. Take a pencil and draw on the paper where you think the magnetic field will appear.
- Sprinkle some iron filings on the paper. Sprinkle the iron filings on the way you would sprinkle salt on your food. Compare where the lines of magnetic force appeared to where you predicted they would appear. Record your observations.
- If you do this activity where there is good ventilation, preferably outdoors, you can spray the pattern with a clear spray lacquer or spray paint. When it dries, you can take the magnet away and the pattern will remain.
- Lift the paper off the magnet. If you did not spray the pattern in place, pour the iron filings back in the jar and fasten the lid securely.
A magnetic field is not flat, but three dimensional. This means that instead of just going in a flat plane like a piece of paper, it also goes up and down. In this activity, you are going to see the pattern of the three dimensional magnetic field.
- Magnet - The best kind of magnet for this activity is a "cow magnet," if you can get one. These are sold at farm supply stores and science education supply stores. If you cannot find a cow magnet, a bar magnet will work.
- Iron filings
- Two-liter plastic bottle
- Paper tube that is the same size as the magnet.
- Remove any labels from the bottle. Wash the bottle and thoroughly dry it.
- Find or make a paper tube just a little bit larger than the magnet. You can cut a toilet paper or paper towel roll, roll it to the right size, and tape it back together.
- Wrap tape around one end of the paper tube until it will plug the neck of the bottle. Stuff the other end of the tube with paper and close it with tape.
- Pour a large amount of iron filings into the bottle, but don't fill it more than about one-third full. Push the paper tube into the neck of the bottle. Leave a little bit sticking out, and tape this part to the neck of the bottle. Shake the bottle and make sure no iron filings fly out.
- What do you think the magnetic field will look like? Draw it as seen from the top and from a side.
- Slip the magnet into the tube. Push some paper in after it so it will not slide up and down in the paper tube. Hold your thumb over the opening and shake the bottle. When you are done, the iron filings will be attracted to the magnet inside the tube and show the three dimensional pattern of the magnetic field.
Design your own experiment!
Do you want to learn more about magnetic fields? Design your own experiment using iron filings and magnets. Be sure to include a hypothesis, procedure and observations. Share the results with your classmates.
The "BIG" magnet
Now that you've seen where the magnetic field of a magnet is, what do you think the magnetic field of the earth looks like?
The picture at the right is a "false color" picture of Earth's magnetic field. The picture was taken from an orbiting NASA satellite. A "false color" picture is where something you can't see is given a false color so you can see where it is. The something you can't see is Earth's magnetic field. A map of Earth has also been inserted into the picture so you can see where Earth is. The picture is looking down at the North Pole of Earth.
How do you think Earth's magnetic field will compare to your magnet's magnetic field?
Can you compare and contrast Earth's magnetic field with your magnet's magnetic field? Write some ways they are alike and some ways they are different. Remember, the color in the photograph is NOT the color of the magnetic field, but is put in to show you where the magnetic field is. The magnetic field itself is invisible.