Problem 2.

The temperature of a body is increased from -173 C to 357 C. What is the ratio of energies emitted by the body per second in these two cases?

Solution:

In this problem we need to use the Stefan–Boltzmann law: the amount of thermal radiation emitted per second by a (black) body is directly proportional to the fourth power of its absolute temperature:

where is a (Stefan-Boltzmann) constant. It is important that in the above expression the temperature is the absolute temperature (measured in Kelvin).

It means that

We convert the temperatures of the body into Kelvin:

Now we can find the ratio of the energies emitted by the body per second: