Physics

The Earth is a huge magnet and, as such, it has a north and a south magnetic pole. Invisible magnetic lines of force leave the Earth near the Geographic South Pole and enter near the Geographic North Pole. For this reason, compass needles always point toward the north. This phenomenon makes it possible for us to use the magnetic field for navigation.

What causes the magnetic field around the Earth? The details are not fully known, but most scientists believe that liquid iron in the outer core rises away from the inner core/outer core boundary due to the very high temperature of the solid inner core. The rising liquid iron causes convection currents that carry the iron across magnetic field lines in the core. This produces electric currents in the highly conductive liquid iron. These currents then produce their own magnetism, which reinforces the Earth’s magnetic field. Because of the spin of the Earth and the variable nature of the convection currents, the Earth’s magnetic field is constantly in a state of flux.

Some places on the Earth experience this flux in the magnetic field more than others. In many of these magnetic-rich regions, the crust is thicker and levels of iron are higher than in other locations. These locations where magnetic fields are strong can sometimes draw compasses away from magnetic north. Many people believe that such magnetic anomalies exist in the Bermuda Triangle, a famous region of the Atlantic Ocean extending from the Florida coast to Bermuda and Puerto Rico. A number of ships and planes have disappeared in the Bermuda Triangle, and magnetic anomalies could account for some of them going missing because compasses on board would malfunction and perhaps cause deadly navigation errors. Although there is no real evidence that unusually powerful magnetic anomalies exist in the Bermuda Triangle, it does make for a good story! In this experiment, you will use magnets to create your own Bermuda Triangle Effect by investigating how magnetic fields can cancel one another.

• small compass
• 3 bar magnets
• 3 colored pencils (red, blue, and green)
• data table

1. Place the bar magnets on the indicated spots on the screen.
2. Place a compass on the screen in the indicated area to put it in contact with a magnet.
3. Observe the direction in which the compass points. Move the red pencil over the indicated area to place a dot on the screen to show the direction.
4. Reposition the compass in the direction the needle points and just beyond the dot you just made.
5. Observe the direction in which the needle is pointing. Place a second red dot on the paper outside the compass case to show the direction that the needle points.
6. Continue to reposition the compass and make red dots until the compass is once again in contact with the magnet.
7. Move the red pencil to the last dot that you marked to draw a smooth curve through the points. Another smooth curve will be drawn for you to give you more information.
8. Repeat the entire procedure for the other two magnets. Use blue for one magnet and green for the other.
9. On your diagram, find and label (using the text box) areas where field lines from the three magnets are close to each other and moving in the same direction. In these regions, magnetic fields are working together.
10. On your diagram, find and label (using the text box) areas where field lines from the three magnets are close to each other and moving in the opposite directions. In these regions, magnetic fields are canceling each other.
11. Put a compass in a region where magnetic fields are moving in the same direction. Describe the behavior of the compass in one of these areas in your data table.
12. Put a compass in a region where magnetic fields are moving in opposite directions. Describe the behavior of the compass in one of these areas in your data table.

1. How did the compass behave in a region where magnetic fields point in the same direction?
2. How did the compass behave in a region where magnetic fields point in opposite directions?
3. How do you think stronger magnets would affect the results?
4. Explain why it could be difficult to navigate by compass in an area with a strong magnetic anomaly.

1. The compass needle points away from the region between the two north ends of the magnets.
2. Answers will vary. The compass may spin and does not point away from north on any magnet.
3. Answers will vary. Stronger magnets produce more pronounced magnetic field lines, but the results would be similar.
4. Answers will vary. Students answers might explain that compass readings in this area might be unreliable, causing a plane or ship to follow an incorrect heading.