Making a Compass Mr. Ahearn 2010

A Brief History The magnetic compass is an old Chinese invention, probably first made in China during the Qin dynasty (221-206 B.C.). Chinese fortune tellers used loadstone to construct their fortune telling boards. Magnetized needles used as direction pointers appeared in the 8th century AD, again in China, and between 850 and 1050 they seem to have become common as navigational devices on ship. The first person recorded to have used the compass as a navigational aid was Zheng He (1371-1435), from the Yunnan province in China, who made seven ocean voyages between 1405 and 1433

Question How do you construct a compass?

Objectives Observe induced magnetism. Build a compass.

Materials Dish/Bowl (clear) Water Dissecting pin (steel) Magnet Cork

Procedure Push dissecting pin through middle of cork stopper. Magnetize the pointed end of dissecting pin with cow magnet. Place pin/cork into water dish. Note orientation of pin (using regular compass) Bring magnet near your compass and pin. Observe the reaction.

domains are oriented randomly and their magnetic fields cancel each other When a strong magnet is brought near the material, the domains line up, and their magnetic fields add together

The Earth's Magnetic Poles The fact that a compass needle always aligns itself in a particular direction, regardless of its location on earth, indicates that the earth is a huge natural magnet. The distribution of the magnetic force about the earth is the same as that which might be produced by a giant bar magnet running through the center of the earth (fig. 1-10). The magnetic axis of the earth is located about 15° from its geographical axis thereby locating the magnetic poles some distance from the geographical poles. The ability of the north pole of the compass needle to point toward the north geographical pole is due to the presence of the magnetic pole nearby. This magnetic pole is named the magnetic North Pole. However, in actuality, it must have the polarity of a south magnetic pole since it attracts the north pole of a compass needle. The reason for this conflict in terminology can be traced to the early users of the compass. Knowing little about magnetic effects, they called the end of the compass needle that pointed towards the north geographical pole, the north pole of a compass. With our present knowledge of magnetism, we know the north pole of a compass needle (a small bar magnet) can be attracted only by an unlike magnetic pole, that is, a pole of south magnetic polarity.

Conclude and Apply Explain why the pointed end of the pin always pointed the same way even if you rotated the dish? Describe the behavior of the compass when the magnet was brought close? Observe the pointed end of the pin. Does it point to the north or south pole of a bar magnet? Infer whether the pointed end of your pin is a north or a south pole. How do you know?

References Bellis, By Mary. "History of the Compass." Inventors. Web. 27 Sept. 2010. <http://inventors.about.com/od/cstartinventions/a/Compass.htm>. Ezrailson, Cathy, Margaret K. Zorn, and Dinah Zike. Electricity and Magnetism. New York: Glencoe/McGraw-Hill, 2008. "Magnetic Poles." Repair and Maintenance Manuals - Integrated Publishing. Web. 27 Sept. 2010. <http://www.tpub.com/neets/book1/chapter1/1g.htm>.