Question

Why is the pendulum of a clock made of Invar (alloy of Iron and Nickel)?
A. Invar has low melting point
B. Invar is non-reactive towards components of air
C. Invar has negligible coefficient of expansion
D. Invar is very delicate

Answer 1

Hint: It should have low or negligible thermal expansion because thermal expansion is the tendency to change its shape, area. The term Invar is derived from the word invariable which means it is not extended or contracted in relation to changes in temperature.

Complete step by step solution:
Invar: Invar, also commonly referred to as \[{\text{FeNi4}}\](\[{\text{64FeNi}}\] in the United States), is a notable nickel-iron alloy for its unusually low thermal expansion coefficient (\[{\text{CTE}}\] or \[\alpha \]). In \[1896\], the alloy was found to have been awarded the Nobel Prize in Physics to the Swiss physicist Charles Édouard Guillaum in \[1920\]. It has made it possible to develop science resources.

Thermal expansion: In response to a temperature change, thermal expansion tends to change its form, area, volume and density without including the transitions of the phase. The average molecular kinetic energy of a material is a monotonic function of temperature. The thermal expansion is caused by the expansion of water due to the higher water temperature. As the oceans collect heat from the atmosphere, the oceans absorb it whenever the atmosphere gets colder. The higher amount would increase the water level in the oceans.

The pendulum clock consists of the invar because the thermal expansion coefficient of the invar is weak or negligible. Thus, despite temperature fluctuations the pendulum length remains unchanged.

Hence, option C is correct.

Note: Invar is suitable for applications where the ambient temperature range includes high dimensionally stable conditions. It is most widely used in high-precision instruments like altimeters, timekeepers and pendulums.