1,792
edits
Changes
→Modern Theory: Planck quantized light, add Lenard
==Modern Theory==
==Modern Theory==
The modern theory of the photoelectric effect is based in the quantum theory proposed by [[Planck]]. In 1905 Einstein applied this to the photoelectric effect, postulating that light was not a continuous wave but a series of discrete packets or quanta of energy distributed over a wavefront. This "discovery of the law of the photoelectric effect" (explaining the effect in terms of quantized energy and providing equations) was the reason the Nobel Prize Committee awarded Einstein the Nobel Prize in 1921.<ref>[http://www.relativitycalculator.com/photoelectric_effect.shtml]</ref> The phenomenon was thus explained as such:
The modern theory of the photoelectric effect is based in the quantum theory proposed by [[Planck]].
In 1900, he published the idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant.<ref>[http://nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.html]</ref> In 1902, Lenard showed that the energy of electrons in the photoelectric effect depended only on the frequency of the incident light. In 1905, Einstein showed that Planck's formula could be used to give a heuristic explanation of Lenard's results. Planck, Lenard, and Einstein all won Nobel Prizes, and Einstein's prize cited his "discovery of the law of the photoelectric effect".<ref>[http://www.relativitycalculator.com/photoelectric_effect.shtml]</ref> The phenomenon was thus explained as such:
* Each photon contained energy based solely on frequency, such that E = hf where h is Planck's constant (6.626 x 10<sup>-34</sup>)
* Each photon contained energy based solely on frequency, such that E = hf where h is Planck's constant (6.626 x 10<sup>-34</sup>)
* Electrons could be emitted if they received sufficient energy from a photon. However, this was an "all or nothing" transfer and emission would only occur if the single photon contained enough energy to overcome the ''work function'' of the material. The minimum frequency to cause emission is known as the ''threshold frequency''
* Electrons could be emitted if they received sufficient energy from a photon. However, this was an "all or nothing" transfer and emission would only occur if the single photon contained enough energy to overcome the ''work function'' of the material. The minimum frequency to cause emission is known as the ''threshold frequency''