Unformatted text preview: The Photoelectric Effect Planck’s outrageous idea really needed some confiimation from a second
experiment. 1887 — Hertz discoveredthat when a beam of UV light fell upon a metal surface
particles capable of conducting electricity are emitted from the metal. 1900 — Lenard: particles emitted are electrons and— -Threshold frequency v.3. Light with frequency below v0 do not eject electrons.
-Electrons ej ect by radiation of frequency V greater than v0 have kinetic energy
proportional to v — v0. -Nuinber of electrons emitted proportional to intensity of the light. 1 905 — Einstein: oscillators in light. source can only have quantis ed energies HP; 1/
(n = 0,1 .13.... ). As oscillators change their energy from nhv to (PI-l )hv emit
radiation of frequency v and energy hv (photon). If the photons energy is more than W then an electron is ejected:
' hv = W + K.E. hvo = W
KB. = h(v—v0) ...
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