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Magnetism – Learning Outcomes
Discuss the nature of magnets. Demonstrate the properties of magnets. Plot the magnetic field of a bar magnet. Demonstrate the Earth’s magnetic field.
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Nature of Magnets Magnets will only attract ferromagnetic materials – iron, nickel, cobalt, and some alloys of these. Magnets are strongest at the ends, called poles. Magnets always have two poles, north (red) and south (blue or black). Cutting a magnet in half creates new poles.
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Nature of Magnets If allowed to rotate freely, a magnet will line up north-south with the Earth. Like poles repel, unlike poles attract. Magnets can create magnetism in ferromagnetic materials.
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Magnetic Fields A magnetic field is the space around a magnet where it has a magnetic effect.
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To Plot a Magnetic Field
Place a bar magnet on a piece of paper. Place a plotting compass near the magnet. Make a pencil mark at the ends of the compass needle. Move the compass so that its needle is pointing towards a dot. Mark the other end of the needle.
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To Plot a Magnetic Field
Repeat moving the compass and marking the needle position. Join the dots with a curve and repeat for another field line.
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Earth’s Magnetic Field
The Earth has a magnetic field due to its molten iron core. We pretend it has a bar magnet in its core with the south magnetic pole at the north geographic pole and the north magnetic pole at the south geographic pole.
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To Demonstrate the Earth’s Field
Hang a bar magnet horizontally in a paper stirrup from a retort stand. Rotate the magnet and let it come to rest a few times. Note the orientation of the magnet each time. Note the poles on the magnet using a compass. Repeat for another magnet.
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To Demonstrate the Earth’s Field
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