Wien's Law

The way the peak of the Planck curve changes with temperature is quantifies by .

This is Powerful!

• Measure the spectrum of the Sun (the intensity of E-M radiation at every wavelength) and find:

  

• Knowing this, we can estimate the surface temperature of the Sun from Wien's Law (this will give the right answer if the solar spectrum does indeed look like a Planck spectrum).

  

What about radiation from humans?

Note that the radiation we are all using to see one another is reflected from the lights in the room (don't believe me? turn off the lights and see what you see).

This is bad news for soldiers and out-of-bounds campers in Yosemite.

What temperature needs to be reached for the Planck radiation of a solid to peak in the x-ray region ( cm)?

Note, solids don't ordinarily get this hot!