Final answer:
The glowing black spot on a heated body is best explained by Stefan's law, which states that the total power emitted by a blackbody is proportional to the fourth power of its temperature.
Step-by-step explanation:
Explanation of Blackbody Radiation
When a body with a black spot (imitating a blackbody) is heated, it begins to emit radiation. According to Stefan's law, also known as the Stefan-Boltzmann law, the total power of radiation emitted by a blackbody across the entire spectrum is proportional to the fourth power of the Kelvin temperature. Therefore, as the body temperature increases, the radiated power also increases significantly, which is why the black spot appears to glow more in a dark room.
Wien's law further states that as a body gets hotter, it emits radiation at shorter wavelengths. This shift towards shorter wavelengths means that the object's color changes from red to blue as its temperature increases.
Option D, Stefan's law, is the correct answer because it directly concerns the increase in total radiated power with temperature, explaining why the black spot glows more when the body is heated.