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# Plotting: What Is The Direction of the Magnetic Lines of Force Around a Magnet?

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Source:
Author: Janice VanCleave

### Problem

What is the direction of the magnetic lines of force around a magnet?

### Materials

• bar magnet
• sheet of paper
• compass
• pencil

### Procedure

NOTE: Never touch a compass with a magnet. Touching a compass with a strong magnet can change the polarity of the compass needle, causing the end marked north to become a south pole and all directions to be reversed.

1. Place the magnet near the bottom edge of the sheet of paper.
2. Place the compass on the paper, about 1 inch (2.5 cm) above the north-pole side of the magnet.
3. Use the pencil to mark a dot on the paper in front of the north pole of the compass pointer.
4. Move the compass forward until the south pole of the compass needle points to the dot.
5. Mark a new dot on the paper in front of the north pole of the compass pointer.
6. Again, move the compass forward until the south pole of its pointer is in front of the second dot.
7. Continue making dots on the paper in front of the compass's north-pole pointer until the compass reaches the south-pole end of the magnet.
8. Repeat the procedure, this time starting at the south-pole side of the magnet.
9. Observe the pattern of the plotted dots.

### Results

The plotted dots form a curved pattern from one end of the magnet to the other.

### Why?

The invisible magnetic field around the magnet is made up of lines of force that move out of the north pole of the magnet and into the south pole. Since "unlike" poles attract each other, the north pole of the compass needle always turns toward the south pole of the magnet. Each time the compass is moved, the compass pointer lines up with the line of force.

### Let's Explore

1. Are there lines of force at the ends of the magnet? Repeat the experiment, this time placing the compass at the comer of the north pole of the magnet.
2. Does the pattern change with different-shaped magnets? Repeat the original experiment using round-shaped and horseshoe-shaped magnets.
3. Do the lines of force cross each other? Repeat the original experiment, placing the compass next to the previous line. Mark the dots as before, and observe the position of the second force-field line. Different lines of force can be plotted by starting the compass in a new position, but you will discover that force lines do not cross each other. Science Fair Hint: Take photographs as you mark each dot in front of the compass pointer. Display the photographs and the plotted dots showing the pattern of the force fields around the side and end of the magnet.

### Show Time!

Is the force field three-dimensional? Magnetize two needles by laying them on a strong magnet for two minutes. Hold the eye end of one needle. Suspend the second needle by touching the points of the two needles together. Slowly move the needles from one end of the magnet to the other. Observe the movement of the hanging needle.

### Check It Out!

The earth behaves as if it contains a large magnet that produces magnetic lines of force around the globe. As the earth revolves around the sun, there are fluctuations in the earth's magnetic field. Think about these questions:

• Why do the major changes in the earth's magnetic field occur during the equinox (when the sun is in line with the earth's equator), while minimum changes occur during the solstice (when the sun is farthest either north or south of the earth's equator)?
• During what months of the year do these major and minor changes take place?