1. The ability of a material or surface to emit thermal radiation, expressed as a ratio compared to an ideal black body.
Usage: physics; technical

Examples

• The emissivity of a black surface is close to 1.0, meaning it radiates heat very efficiently.
• Shiny metals have low emissivity and reflect most thermal radiation rather than emitting it.
• Engineers must account for the emissivity of different materials when designing thermal systems.
• The emissivity value depends on both the material and the temperature of the surface.
• Infrared cameras use emissivity data to accurately measure the temperature of objects.