# How is E-M radiation produced?

(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 radiations

• ``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 point!

• For a given object, as the temperature increases:

1. The Intensity of radiation at all wavelengths increases

2. 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.

# Wien's Law

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).