What material composition is typical for Invar tapes used in surveying?

• A. 50% nickel and 50% steel
• B. 35% nickel and 65% steel
• C. 30% nickel and 70% steel
• D. 100% steel

Answer: (B)

Invar tape is a type of measuring tape that is specifically manufactured to maintain a very low coefficient of thermal expansion, making it ideal for precise surveying measurements where temperature changes could affect accuracy. The composition of Invar is typically around 36% nickel and 64% iron, but in context with this question, the closest representation in the choices provided is the option that indicates 35% nickel and 65% steel.

This mix is effective because the presence of nickel significantly reduces the expansion rates of the tape material under varying temperatures. By avoiding excessive thermal expansion, Invar tapes help ensure that the measurements taken are stable and reliable, which is crucial in surveying work where precision is paramount. The other choices, whether they suggest an incorrect percentage balance of nickel and steel or suggest materials that do not include the necessary nickel content, do not provide the same thermal stability required for surveying accuracy.