Why are rheostats made of high resistivity wire? What is the disadvantage of a rheostat with a copper wire winding?

According to the formula for the resistance of the conductor: R = pl / S. those. the greater the resistivity of the metal, the shorter the conductor length must be used. Copper has a very low resistivity, so a rheostat with a copper wire winding would have a very long wire inside and therefore would be very expensive.

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