00:01
Okay, in this question we're talking about using light as a source of heating.
00:07
So we're going to have three concept questions, a, b, and c.
00:10
And then we're going to have a more quantitative question.
00:16
We should hopefully back up what we're found in parts a, b, and c.
00:21
So in this question, we're told that there's some plate, which we're going to hit with radiation, which will raise the temperature of the plate.
00:32
First, i just want to find a formula for heat in terms of the mass, the heat capacity of the material, and the amount of temperature that we want to change.
00:45
This formula is just mc delta t.
00:50
All right, and in question b, they ask us, is the energy per photon greater or smaller for infrared light or visible light? so we need to relate energy to wavelength somehow.
01:07
So we know that e is equal to hc over lambda.
01:13
So e is proportional to one over lambda.
01:17
And since the wavelength is greater for infrared than for visible light, the energy of visible light is greater than the energy of infrared light.
01:27
Start circling my answers, doing some abundant and clear.
01:32
Okay, and then in question c they ask us, is the number of photons required to raise the plates a certain temperature greater or smaller for infrared or for visible light? well, here we see that there's more energy for photons of visible light, so we're not going to need as many of them as we are for infrared...