Materials ___ emit thermal energy well.

• A. Without emissivity
• B. With high emissivity
• C. With low emissivity
• D. That are reflective

Answer: (B)

Emissivity describes how effectively a surface emits thermal radiation compared to a perfect blackbody. Materials with high emissivity release more infrared energy at a given temperature, so they are good at emitting thermal energy. Conversely, low emissivity means the surface is a poor emitter and tends to reflect or retain heat rather than radiate it. Reflective materials typically have low emissivity, so they don’t emit heat as well. Therefore, the best fit is high emissivity, which indicates a surface emits thermal energy well.