Which statement best describes the metals used in the described bimetal strip?

Which statement best describes the metals used in the described bimetal strip?

• A. Copper and aluminum
• B. Iron and nickel
• C. Copper or brass and Invar
• D. Silver and gold

Answer: (C)

A bimetal strip works because two bonded metals have different rates of expansion when heated. When temperature rises, the metal that expands more lengthens enough to bend the strip toward the metal that expands less. Invar is famous for its very low thermal expansion, so pairing it with a metal that expands more—such as copper or brass—produces a reliable bend with temperature. That combination of copper or brass with Invar is exactly why this pairing is described for the metals in a typical bimetal strip. Other options don’t capture that practical pairing: they either use metals that don’t provide the distinct differential expansion in this context, or involve materials not commonly used together in standard bimetal applications.

A bimetal strip works because two bonded metals have different rates of expansion when heated. When temperature rises, the metal that expands more lengthens enough to bend the strip toward the metal that expands less. Invar is famous for its very low thermal expansion, so pairing it with a metal that expands more—such as copper or brass—produces a reliable bend with temperature. That combination of copper or brass with Invar is exactly why this pairing is described for the metals in a typical bimetal strip. Other options don’t capture that practical pairing: they either use metals that don’t provide the distinct differential expansion in this context, or involve materials not commonly used together in standard bimetal applications.