L07 Chem 111A Lecture Notes - Lecture 7: Superposition Principle, Wind Wave
13 Dec 2016
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4 September 2015
Lecture 7: Wave-Particle Duality of Light
I. Single Slit Experiment
A. If light behaved as particles
1. From a (single λ) light source, light particles would shoot out in all directions, but a
screen with a slit would direct one path/stream of light particles
2. They expected to see just one narrow hump in intensity here
3. Wrong
B. Water Analogy
1. With plane waves like water waves and a wave breaker
2. At the wave break, waves will start to bend and diffuse: diffraction of waves
C. What they observed
1. A (single λ) light source was set up so planar waves head towards a slit (width “d”)
and the waves were diffracted (λ doesn’t change), and saw the following intensity:
2. The smaller the slit width (d), the broader the diffraction peak wave, this also depends
on λ
a. Diffraction occurred (roughly) for λ/2 ≤ d ≤ 10λ
b. Also to determine diffraction breadth, must account for distance from slit to
detection screen (L)
II. Double Slit Experiment
A. If light behaved as particles
1. With a single λ light source, now 2 slits and they expected just 2 narrow intensity
peaks corresponding with the slits (if light acted as a particle)
2. Wrong
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