This lesson explores the zinc–copper alloy used in modern coinage, focusing on the U.S. one-cent coin (penny) produced after 1982. Students will examine how the transition from solid copper to zinc-based alloy reduced production costs, and how XRF spectroscopy reveals the layered composition of plated metals. The lesson introduces the concept of plating and its impact on XRF results.
Objectives
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Understand the composition and properties of zinc–copper alloys used in coinage.
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Recognize the difference between true alloys and plated metals.
Materials
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U.S. one-cent coins (pre- and post-1982)
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Sandpaper or abrasive tool
Lesson Plan
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Discuss the historical change in the composition of the U.S. penny and reasons for adopting a zinc-based alloy.
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Perform XRF analysis of the coin surface and discuss spectral peaks for copper and zinc.
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Lightly abrade the coin surface and reanalyze to reveal the underlying zinc-rich alloy.
