Graphics Reference
In-Depth Information
Diffraction grating
Heat source
Narrow slit lets just
one wavelength pass
Figure 26.3: An object is heated to some temperature, and a narrow beam of the radiation
it produces is focused on a diffraction grating, splitting it into energies of different wave-
lengths. By moving a plate with a slit in front of this diffracted energy, we can measure the
energy radiated in a narrow range of wavelengths,
[
λ
,
λ
+
d
λ
]
.
x
10
5
16
14
8
6000
K
12
10
8
5000
8
K
6
4
4000
8
K
2
0
0
500
1000
1500
2000
2500
3000
Wavlength (nm)
Figure 26.4: The radiation near wavelength
λ
from a black body heated to some tem-
perature T, plotted as a function of
λ
, shown for several values of T. The shaded region
indicates the wavelengths of visible light.
Inline Exercise 26.1:
On a warm day the temperature is about 300
◦
K.
(a) What does the Stefan-Boltzmann law predict as the amount of energy radi-
ated from your body? (You should assume that your surface area is about one
square meter, and that you radiate as a black body.)
(b) When sitting at home on such a day, why do you not get very cold from
this loss of heat?
