Compared to a blackbody at the same temperature, the emissivity of a real surface is:

Compared to a blackbody at the same temperature, the emissivity of a real surface is:

• A. Greater Than A Blackbody
• B. Equal To A Blackbody
• C. Less Than A Blackbody
• D. Emissivity Can Exceed 1

Answer: (C)

Emissivity is the ratio of a surface’s actual thermal emission to the emission of a perfect blackbody at the same temperature. A blackbody is an ideal emitter, absorbing all incident radiation and radiating the maximum possible amount. Real surfaces aren’t perfect emitters—they reflect and sometimes transmit some energy—so they emit less than a blackbody. Since emissivity cannot exceed 1, real materials have emissivity less than a blackbody in general.

Emissivity is the ratio of a surface’s actual thermal emission to the emission of a perfect blackbody at the same temperature. A blackbody is an ideal emitter, absorbing all incident radiation and radiating the maximum possible amount. Real surfaces aren’t perfect emitters—they reflect and sometimes transmit some energy—so they emit less than a blackbody. Since emissivity cannot exceed 1, real materials have emissivity less than a blackbody in general.