What causes the expansion of metals when heated?
The correct answer and explanation is:
The expansion of metals when heated is primarily caused by the increase in the kinetic energy of their atoms or molecules. When a metal is heated, the temperature increases, causing the atoms or molecules within the metal to vibrate more rapidly. These increased vibrations cause the atoms to move further apart from one another, leading to an overall expansion of the material.
At a microscopic level, metals are made up of a regular arrangement of atoms held together by metallic bonds. These bonds involve a “sea” of free-moving electrons that allow the atoms to slide past each other more easily than in other types of solids. As the metal heats up, the increased energy makes the atoms vibrate with greater amplitude. This causes the average distance between the atoms to increase, thereby increasing the volume of the metal.
The degree of expansion depends on several factors, including the type of metal, its structure, and the temperature range. Different metals have different coefficients of thermal expansion, which is a measure of how much the material expands per unit length for each degree of temperature increase. For example, metals like aluminum expand more than metals like steel when heated, because their atomic structures and bonding types are different.
The expansion can be observed in practical applications, such as in the design of railway tracks, bridges, and pipes, where allowances are made for the expansion and contraction of metals due to temperature changes. The expansion is a fundamental property of matter that is important to understand for various engineering and construction projects, ensuring that materials perform optimally and safely under changing temperature conditions.