Chapter 31 Light Quanta

Light as a Particle Called a photon E = hf

Photoelectric Effect Certain metals will emit electrons when exposed to light. See the Effect

Photoelectric Effect No time lag between turning on light and emission of electrons Works for short wavelengths but not long wavelengths. Number of electrons µ number of photons

Wave-Particle Duality Light can act as a wave Interference Diffraction Holography Light can act as a particle Photoelectric Effect No experiment can show both natures at the same time.

Light as a Wave E  1/l E  p l  1/p l = h/p

De Broglie Wavelength Particles as waves Why don’t we see it? l = h/ p A typical bullet (m = 0.02 kg, v = 330 m/s) has a de Broglie wavelength of 10-34 m

De Broglie Wavelength But an electron traveling at 2% c has a de Broglie wavelength of… 10-10 m = 1 Å = about the size of an atom

Uncertainty Principle There is a relationship between how well you can measure position and motion If you want to measure where a particle is, you cannot know how fast it is moving Also a joint uncertainty between energy and time