(1) Accelerate charged particles back and forth like they do at the radio station.
(2) All objects with temperature above ``absolute zero'' emit E-M
- ``Absolute Zero'' is the temperature where all motion (on the
atomic level) ceases.
- 0 Kelvin = -459F = -273C
- If a plot is made of the amount (intensity) of E-M radiation
emitted at each wavelength by a non-zero-temperature solid object,
this is called a ``spectrum''. For solids, the spectrum is called
a ``Planck'' or ``blackbody'' spectrum. This is an important
- For a given object, as the temperature increases:
- The Intensity of radiation at all wavelengths increases
- The PEAK of the intensity moves to Shorter wavelengths
(or Higher frequencies). You already knew this - think about your
stove element as you turn up the heat.
The way the peak of the Planck curve changes with temperature is
quantifies by Wien's Law .
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).
Q. 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.
Q. 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!
Wed Jan 14 23:06:17 PST 1998