The total electromagnetic radiation from an object consists of which components?

• A. Reflected only
• B. Transmitted only
• C. Emitted, transmitted, and reflected
• D. Absorbed and emitted

Answer: (C)

The total electromagnetic radiation leaving an object comes from three paths: what the object itself emits due to its temperature, what passes through the object if it’s transparent at that wavelength, and what is reflected off the surface. Emission is the thermal glow the object emits; transmission is energy that makes it through the material and exits on the other side; reflection is the portion of incident light that bounces back. Absorbed energy is energy taken in, not radiated away, though in thermal equilibrium absorbed energy is related to emission by Kirchoff’s principle. So the overall radiative output is the sum of emitted, transmitted, and reflected energy.