Question

What is the value of emissivity for tarnished copper?

(a) 0.78

(b) 0.77

(c) 0.76

(d) 0.75

This question was addressed to me by my school principal while I was bunking the class.

My question comes from Emissivity in section Modes and Diffusion of Mass Transfer

Answer 1

Right option is (d) 0.75

Easiest explanation: This is optically thick material. The absorptivity at the wavelengths doesn’t depend on the thickness of the material.