Electricity and Magnetism Science Fair Projects, Revised and Expanded Using the Scientific Method by Robert Gardner

Author:Robert Gardner [ Gardner, Robert]
Language: eng
Format: epub
ISBN: 978-1-4645-0191-3
Publisher: Enslow Publishers, Inc.
Published: 2010-10-15T00:00:00+00:00

Earth as a Magnet

The fact that a compass needle points in a northerly direction suggests that Earth behaves like a giant magnet, as shown in Figure 19. Suppose you were to take a compass to the Boothia Peninsula, north of Hudson Bay, in northern Canada, about 1,200 miles from Earth’s geographic North Pole. There, at about 76 degrees latitude, 100 degrees west longitude, you would find the compass needle points straight down, indicating it is over one of Earth’s magnetic poles. But think! If the north-seeking pole of your compass points downward at this pole, is Earth’s magnetic pole under Boothia Peninsula a north-seeking or a south-seeking pole?

Similarly, suppose you took a compass to a point in Antarctica near Dumont d’Urville, about 1,200 miles from Earth’s geographic South Pole. There, at about 67 degrees latitude, 140 degrees east longitude, you would find the compass needle’s north-seeking pole pointing straight up. Is Earth’s magnetic pole in Antarctica a north-seeking or a south-seeking pole?

Since Earth’s magnetic poles are not located at its north and south geographic poles, compass needles seldom point toward true north. Within half a degree, the North Star is directly above our North Pole. At night, a compass needle is not likely to point in the direction of the North Star. For example, a compass near Boston, Massachusetts, will point about 15 degrees west of true geographic north. A compass near San Diego, California, will point about 15 degrees east of true geographic north. But there are points where a compass needle does point toward true north. Such a region lies along the Georgia-South Carolina border.

The difference between true geographic north and magnetic north is called the magnetic declination. However, Earth’s magnetism is constantly changing. Therefore, charts showing the angles of magnetic declination on Earth’s surface have to be revised frequently.

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