physics question #1208



E.H., a 0 year old n/a from AOL asks on January 21, 2003,

Q:

I understand about the Curie tempurature but I am wondering if an electromagnet has a Curie temperature and if so is there another way to figure it out then trial and error?

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the answer

James Livingston answered on January 22, 2003, A:

The term "Curie temperature" only applies to a ferromagnet, not an electromagnet. As the temperature of a ferromagnet like iron increases, eventually you reach a temperature where the "exchange force" coupling the magnetism of neighboring atoms is overcome by thermal energy, and ferromagnetism disappears rather abruptly (although iron remains a paramagnet above its Curie temperature (1414 degrees Fahrenheit).

In an electromagnet, the magnetism results not from atomic magnetism, but from electric current flowing through the windings. Most electromagnets have copper windings, and there is no particular temperature at which copper loses its ability to carry electric current. However, the electrical resistance of copper does increase with increasing temperature, so it will require more and more voltage to produce the same current and magnetic field. And of course, if the temperature gets high enough, the copper wires will eventually melt.

If the electromagnet instead has superconducting windings, its operation will be limited to temperatures below the "critical temperature" for superconductivity, but that is different from the "Curie temperature" of ferromagnets.

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