The common United States penny found in circulation today will not be attracted to a standard magnet. This lack of attraction is due entirely to the coin’s elemental composition, which lacks the necessary characteristics for a strong magnetic response. Understanding this phenomenon requires examining the materials used in modern coinage and the specific science that governs how metals react to a magnetic field.
What Are Pennies Made Of?
The material composition of the US penny has changed significantly over time, directly impacting its interaction with magnets. Since 1982, the penny has been produced with a copper-plated zinc core, consisting of 97.5% zinc and 2.5% copper. This change was an economic decision driven by the rising cost of copper in the early 1980s. Pennies minted before mid-1982 were primarily composed of a bronze alloy (95% copper, 5% zinc and tin). Neither the modern zinc-dominant penny nor the older copper-dominant penny contains the elements necessary for a strong magnetic pull.
The Science of Attraction
A strong, noticeable attraction to a magnet is a property called ferromagnetism, which is limited to only a few elements like iron, nickel, and cobalt. These metals possess unpaired electrons that spontaneously align into microscopic regions known as magnetic domains. When an external magnet is brought near, the domains align, causing the material to be strongly pulled toward the magnet.
Neither copper nor zinc possesses this structure for ferromagnetism. Copper and zinc are instead classified as diamagnetic materials, meaning they are very weakly repelled by a magnetic field. This repulsion is so faint that it is undetectable without specialized laboratory equipment. The copper and zinc used in pennies are considered non-magnetic.
The Notable Exception: The 1943 Steel Penny
There is one historic exception to the rule that US pennies do not stick to magnets: the 1943 Lincoln cent. Due to the high demand for copper during World War II, the United States Mint temporarily changed the penny’s composition to conserve metal for military supplies. For this one year, the penny was struck using a zinc-coated steel planchet. Steel is an alloy that contains a significant amount of iron, which is a ferromagnetic element. Because of its iron content, the 1943 steel penny will stick strongly to a magnet, making it the only regular-issue US coin that exhibits this property.