Two perfectly absorbing spheres have radii of R and 3R. Both are held at the same temperature. The flux of radiant energy emerging from each square meter of the larger sphere is
A) the same as the flux from the smaller sphere.
B) 3 times the flux from the smaller sphere.
C) 9 times the flux from the smaller sphere.
D) 27 times the flux from the smaller sphere.

Question

Quizplus · Accepted Answer

The flux of radiant energy per unit area is determined by the Stefan-Boltzmann law, which states that the energy radiated per unit surface area of a black body is proportional to the fourth power of its temperature. Since both spheres are at the same temperature and the law does not depend on the size of the object, the flux from each square meter of both spheres will be the same.

Two Perfectly Absorbing Spheres Have Radii of R and 3R