Which statement defines the coefficient of thermal expansion?

• A. The size of a material changes with a change in temperature.
• B. It remains constant with temperature.
• C. It is determined solely by color.
• D. It measures electrical capacity.

Answer: (A)

The coefficient of thermal expansion tells you how much a material’s size changes as temperature changes. When temperature rises, atoms vibrate more and typically spacing increases, so length, area, or volume expands; when temperature falls, it contracts. The coefficient is the fractional change in size per degree of temperature change (for a linearly measured dimension, ΔL ≈ α L0 ΔT, with α = ΔL/(L0 ΔT) and analogous definitions for area and volume). So the statement that the size of a material changes with a change in temperature captures exactly what the coefficient describes. The other ideas aren’t definitions of it: the coefficient isn’t a fixed value across all temperatures, it isn’t determined by color, and it isn’t about electrical capacity.