Help please.

Question

How does quantum theory explain blackbody radiators?
A. Raising the temperature results in the radiator giving off photons of high-energy ultraviolet light.

B. As the radiator is heated, it can have only certain specific temperature values.

C. Raising the temperature of the radiator causes more photons of a few possible energies to be emitted.

D. As heat is added, the radiator emits photons across a wide range of visible-light frequencies.

Answer 1

At higher temperature, the blackbody emits radiation at higher intensity and shorter wavelength (higher frequency).  As the body gets hotter, the peak of the radiation curve shifts toward the ultraviolet end of the spectrum.

 

(B) is incorrect, as there is no limit to how high the temperature of the blackbody can get.

(C) is incorrect, because the very definition of a blackbody is that it absorbs and emits radiation over the entire range of the electromagnetic spectrum.

(D) is partially correct in that the blackbody emits over a wide range of visible-light frequencies, but it does not answer the emergence of invisible radiation (e.g. ultraviolet) at higher temperature, or the emission of infrared and radio waves at lower temperature..

 

(A) is the best answer.  It is true, and it explains the so-called "ultraviolet catastrophe" observed in blackdody radiation, which classical radiation theory could not explain.  It was the investigation of this catastrophe that led to the development of quantum theory.