Dual Nature of Radiation and Matter

About this unit

Light behaves as a wave in interference and diffraction, yet some experiments can only be explained if light comes in packets of energy called photons. This unit studies that particle nature through the photoelectric effect: the observations of Hertz and Lenard, the failure of wave theory, and Einstein's photoelectric equation. It then turns the idea around: if waves can behave like particles, particles such as electrons can behave like waves. De Broglie's relation gives the wavelength of a moving particle, and electron diffraction experiments confirm it. This dual nature leads naturally into the next unit on atoms.

How to prepare

Learn the four experimental laws of the photoelectric effect and which ones wave theory cannot explain. Memorise Kmax = hν – φ₀, eV₀ = Kmax, φ₀ = hν₀ and hc ≈ 1240 eV nm. Learn λ = h/p and λ = 1.227/√V nm for electrons. Practise graphs of photocurrent against potential and stopping potential against frequency, and quick numericals in eV.