Which statement about radiant heat from an exposed surface is accurate?

• A. Creating a Vacuum Will Stop Radiant Heat.
• B. Materials that reflect radiated energy help increase radiant heat.
• C. Dark materials emit and absorb heat more effectively than light materials.
• D. Temperature differences between the heat source and exposed surface have no impact.

Answer: (C)

The key idea is how radiant heat interacts with surfaces through absorption, emission, and reflection. Dark, matte materials tend to have higher emissivity, meaning they absorb radiant energy more readily and also emit radiation more efficiently at a given temperature. Because absorptivity and emissivity are linked properties for opaque surfaces (Kirchhoff’s principle), a surface that absorbs well will also emit well. So a dark material will heat up faster when exposed to radiant heat and will radiate heat away more readily than a light material, making the statement about dark materials being better at emitting and absorbing radiant heat the best choice.

The other ideas don’t fit because: radiant heat can travel through a vacuum, so creating a vacuum does not stop it; reflective or light surfaces tend to reflect rather than absorb, reducing radiant heat transfer; and radiant heat transfer depends on temperature differences—larger differences drive more energy flow.