Comparative emissivity: The emissivity of a polished silver surface, when compared to an ideal black body at the same temperature, is generally considered to be…

Introduction / Context:
Emissivity strongly influences radiative heat transfer. Highly reflective metals like polished silver are widely used in thermal insulation and radiation shields precisely because of their low emissivity.

Given Data / Assumptions:

• Comparison at the same temperature and broad thermal radiation wavelengths.
• Black body emissivity is 1 by definition.
• Polished silver has high reflectivity in the infrared spectrum.

Concept / Approach:
Emissivity is the ratio of a real surface’s emissive power to that of a black body at the same temperature. A polished silver surface reflects most incident radiation and emits poorly. Thus, its emissivity is much less than 1 and is commonly referred to as very low (on the order of 0.02–0.05 depending on finish and temperature).

Step-by-Step Solution:

Verification / Alternative check:
Radiation heat-transfer handbooks list emissivity values for polished metals significantly below 0.1, confirming the “very low” classification compared with a black body.

Why Other Options Are Wrong:

Same/high/greater than 1 contradict both measurement and theory.“Low” is qualitatively true, but “very low” better reflects the known magnitude for polished silver.

Common Pitfalls:
Assuming shiny appearance alone defines emissivity across all wavelengths; surface oxidation or roughness can raise emissivity, but polished silver remains very low relative to a black body.

Final Answer:

very low