Background
Quantum energy
|
Science strides through revolutions, but people often refuse to accept revolutionary concepts at first place. This describes the emergence of the Planck's equation. In classical physics, energy of electromagnetic (EM) radiation was thought to be absorbed or emitted continuously. It wasn't until late 1900 the German scientist Max Planck (1858-1947) made a radical assumption in explaining the black body radiation spectrum, the idea of discrete energy arose. In Planck's assumption, radiant energy is emitted in small bursts, known as "quanta". Each of the bursts called a "quantum" has energy E that depends on the frequency f of the electromagnetic radiation by the equation: |
 Photo of Max Planck. Courtesy of AIP Emilio Segre Visual Archives, W.F. Meggers Collection. |
where h is a fundamental constant of nature, the "Planck constant".
This equation is later found to be true for all EM radiant energy emitted or absorbed.
Planck's equation implies the higher the frequency of a radiation,
the more energetic are its quanta. It for example explains why you can never
get brown from visible light ((
to 
),
but from ultraviolet light (from 
to 
).
The quanta of visible light don't carry enough energy to start the chemical reaction
in your skin!
Figure: Visible Spectrum.
Courtesy of NASA.
The quantum energy is not to compare with the power of the light! The Power of light (Luminosity) is the total energy per second, that means the number of quanta per second times the quantum energy. Therefore even if visible light carrys a lot more Energy per second than UV-light, you won't get any browner from it.
The theoretical black body radiation spectra predicted
by Planck's Radiation Law, with the assumption |
|
 Photo of Max Planck with his hand writing. Courtesy of the Archives, California Institute of Technology. |
Many other scientists, including Wien, Rayleigh and Jean, attempted to explain the blackbody radiation spectra using classical wave theory and failed. However, the idea of quantized energy was too revolutionary for most scientists at the time (Even Planck puzzled his own conclusion). It was not generally accepted until 1905 when Einstein extended Planck's equation in deriving his formula for photoelectric emission. The idea of quantized energy led Einstein to postulate the particle-wave duality of light and other EM radiation. Planck's equation is essential to the formulation of quantum physics. |
Gravitational
potential energy 
Black
body radiation[Interactive] | [Biography] | [Guest Book] | [Help] | [About]
"Black holes aren't black - After Hawking they shine!"
Presented by Angie, Matthias and Thorsten
Team C007571,ThinkQuest Internet Challenge 2000.
Last modified: 2000-08-09.