Most objects at the temperatures that we live
in emit their peak radiation in infrared (IR). This is why the military
has developed infrared goggles for night combat. However, the temperature
and emissivity of an object determines how intensely it will be seen at
a given IR frequency. In this experiment the student uses an IR camera
to determine temperatures and emissivities of different objects.
The student starts by setting up the camera to image a black can first
filled with tap water, then with hot water, to measure the temperature difference.
Next the student sets the IR camera to image five samples -- two references:
a microscope slide coated with aluminum (low emissivity), and a microscope
slide painted with flat black paint (high emissivity); and three target
samples, including a stainless steel bar. For the first look at these
object, the student sets up a "hot" background by placing a container of
hot water behind the targets. This serves to make the background
term dominant in the calculations. Then the student looks again at
the objects, this time using a container of liquid nitrogen to make a "cold"
background. This serves to make the background term negligible in
the calculations. Finally the student images the steel bar at two
temperatures, heating it up using a heat gun. Then, using the emissivity
calculated from the hot and cold background images, the student measures
the final temperature of the steel bar.
Click here to see an image taken from the IR camera