Problem #0004 Quantum Physics Problem #0006 Chapters Chapters


Problem 49.12 (RHK)

A thermograph is a medical instrument used to measure radiation from the skin. For example, normal skin radiation at a temperature of and the skin over a tumour radiates at a slightly higher temperature. (a) We have to derive an approximate expression for the fractional difference in the radiant intensity between adjacent areas of the skin that are at slightly different temperatures and . (b) We have to evaluate this expression for a temperature difference of . We may assume that skin radiates with a constant emissivity.

Solution:             Click For PDF Version


We use the Stefan-Boltzmann law for the radiant intensity :


where is the emissivity and the Stefan constant




We next workout the expression for and .

We find