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Penny - headsIntroduction: Think of the penny shown in the diagram. You might have heard that the penny is composed of copper. However, the penny was only made of pure copper from 1783 to 1837. The composition of the penny changed, consisting of alloys, or physical mixtures of different metals. After 1982, the composition of the penny as an alloy changed to the composition that we know today - 97.5% zinc and 2.5% copper. However, pennies are not the only alloy that we encounter in everyday life. Other examples of alloys include stainless steel, bronze, all gold that is used in jewelry, and brass.

Alloys, being a physical mixture of two or more metals in solid form, will tend to retain properties of the original components. This idea of a mixture retaining its original properties can help to explain some of the observed properties of alloys. One such property is the fact that alloys do not have a single melting point, but rather a range of temperatures in which the alloy will melt, with the alloy being a mixture of the solid and liquid phases. Because metals in an alloy tend to have different melting points characteristically, the mixing of these metals will lead to different parts of the alloy melting at different times, leading to the solid and liquid phases existing simultaneously.

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