Light

QMI

Planck’s Proposal

Proposal

Light is emitted in quanta of energy… $E=h\nu$ $v\to$(nu) Light’s frequency in Hz (Hertz) $h\to$ Planck’s constant

Planck

$h=6.62606957\times 10^{-34}Js$ (Joule seconds)

Photoelectric Effect

• Shining ultraviolet light on the metal plate gives flow of negative charge (Hertz, 1887)
• Flow can be stopped with a specific voltage independent of the brightness but dependent only on the frequency (Lenard, 1902)
• Einstein’s Proposal (1905): Light is made up out of particles, photons of energy. The kinetic energy of emitted electrons is the energy left over after the electron has been “lifted” over the work function barrier.