Infrared radiation is directed
toward an object. The object absorbs the infrared
radiation and then emits it. Which of the following diagrams
best represents the behavior of the object?
In these three different diagrams,
we see three different representations for how this infrared radiation absorption
and emission occurs. In all three, infrared radiation is
incident on the surface from above. The difference between them comes
down to how infrared radiation is then emitted. The key point for us to realize is
that before infrared radiation can be emitted, it must first be absorbed.
Note that in option (A), the
emitted radiation seems to be reflected off of the surface. The incoming and outgoing radiation
follow a path we would expect for a reflected light ray. Infrared radiation is light, light
that our eyes aren’t sensitive to. But as we mentioned, for infrared
radiation to be emitted, it must first be absorbed. We can say then that option (A) is
not an accurate reflection of this process.
In option (C), the radiation seems
to pass right through the surface. When this happens to infrared
radiation, we would say that that radiation is transmitted. If that happens, though, this
infrared radiation here is not really being emitted. It’s not being taken in, we could
say, to this object and then radiated out. If answer option (A) represented
reflection, answer option (C) represents transmission. Neither of those processes involves
Answer option (B) best represents
an object that first absorbs and then emits infrared radiation. Note that absorbing this infrared
radiation will tend to increase the temperature of the object. We know from experience that a
heated object will tend to radiate out in all directions, and we see that in this
example. Our final answer is option (B).