21.2 Electromagnetism

You know that unlike electric charges attract one another and that like electric charges repel one another. It is easy to discover a similar effect with the north and south poles of two magnets. However, it's much more difficult to figure out the relationship between electricity and magnetism. In fact, the connection was discovered accidentally by the Danish scientist Hans Christian Oersted in 1820.

One evening Oersted, pictured in Figure 6, was conducting scientific demonstrations for his friends and students in his home. One demonstration used electric current in a wire, and another used a compass needle attached to a wooden stand. As Oersted turned on the current for the electricity demonstration, he saw the compass needle move. When he turned off the current, the needle moved back to its original position. Further investigation showed that the current in the wire produced a magnetic field. Oersted had discovered a relationship between electricity and magnetism.

Figure 6 In 1820 Hans Oersted discovered how magnetism and electricity are connected. A unit of measure of magnetic field strength, the oersted, is named after him.

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