Photon model of light
A quantum mechanical description of light as discrete packets of energy called photons, each with energy E = hf = hc/λ and momentum p = h/λ. The photon model explains phenomena like the photoelectric effect that the classical wave model of light cannot account for.
Formula
E = hf = hc/λ
Real World
Solar panels work because individual photons of sunlight knock electrons free in silicon — Einstein won his 1921 Nobel Prize for explaining this photoelectric mechanism, not for relativity.
Exam Focus
If asked why increasing intensity doesn't increase maximum KE, explain that each photon acts individually on one electron.
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