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Wave Nature of Matter

 

Einstein and the Photoelectric Effect

 

ð Light shining on material causes emission of electrons - consistent with the wave theory

ð But, can also be explained by the particle theory

 

The details of the photoelectric effect were in direct contradiction to the expectations of very well developed classical physics.

The explanation marked one of the major steps toward quantum theory.

The remarkable aspects of the photoelectric effect when it was first observed were:

1. The electrons were emitted immediately - no time lag.
2. Increasing the intensity of the light increased the number of photoelectrons, but not their maximum kinetic energy.
3. Red light will not cause the ejection of electrons, no matter what the intensity.
4. A weak violet light will eject only a few electrons, but their maximum kinetic energies are greater than those for intense light of longer wavelengths.

 

 

Young's Double Slit Experiment (next chapter, The Wave Theory of Light)

Exhibited a typical wave interference pattern as opposed to particles passing through each slit

Wave-Particle Duality

 

Sometimes one, sometimes the other.

Observe me and I will become a particle, otherwise I am probably a wave.

But what is meant by "observe"?

 

The evidence for the description of light as waves was well established at the turn of the century

The the discovery of the photoelectric effect introduced firm evidence of a particle nature as well.

The particle properties of electrons became well documented

Then along came DeBroglie (chapter 27) and the subsequent experiments by Young (chapter 24) and others that established the wave nature of the electron.

 

 

Phenomenon Can be explained in terms of waves.     Can be explained in terms of particles.
Reflection    
Refraction*    
Interference    
Diffraction*    
Polarization*    
Photoelectric effect    

* Refraction (Snell's Law), Diffraction (waves travelling around an object - next chapter), polarization (light exhibits different properties in different directions - next chapter)