Modern Physics - 20th Century

 

  • fundamental nature of light & electromagnetic radiation

 

  • origins & destiny of universe

 

  • parts of the atom

 

  • How energy is absorbed and emitted by electrons

 

  • gravity


I. Dual Nature of Light - Light appears to exhibit 2 characteristics:

Wave or Particle

 

A. Review - 19th Century -

Experiments supporting wave theory

 

1) Interference - "Double Slit Exp." - constructive/ destructive

2) Polarization - "Filtering of Light - Light waves have orientations


3) Diffraction - Spreading out of Light behind a barrier


4) Doppler - Color Shift of Light - "Blue to, Red Away"

 

B. Experiments Supporting Particle Theory of Light (20th century)

 

Experiment in the late 1800's baffles scientists.


Light is not acting like a wave!


Experiment scientists can't explain is called…
 The Photoelectric Effect

- when light is exposed to the surface of certain metals,
 the light energy is absorbed and   electrons are ejected

Light
(or other electromagnetic radiation)

Emitted electrons are called PHOTOELECTRONS
 

Photosensitive metal

The light’s energy causes
 the emission of electrons