The thermal expansion concept is defined as which of the following?

• A. An increase in a material's physical dimensions due to heat
• B. A decrease in dimensions due to cooling
• C. No change in size with temperature
• D. A change in color with heating

Answer: (A)

Thermal expansion is the tendency of materials to increase in size when temperature rises. As temperature goes up, particles vibrate more and push outward, causing length, area, and volume to grow. The amount of change depends on the material and the dimension considered, described by the linear expansion relation ΔL ≈ α L0 ΔT (where α is the linear expansion coefficient). For volume, ΔV ≈ β V0 ΔT with β ≈ 3α for many solids.

So the best description is: heating leads to an increase in a material’s physical dimensions. The other options describe opposite behavior (contraction with cooling), no size change, or a color change, which are not the definitions of thermal expansion.