1. Wave Nature of Light
So far, we’ve studied some elements of the nature of light: reflection, refraction

2. Isaac Newton In his day, Newton was most famous for his work on light.
He described light as a beam of ultra-tiny particles.
This could explain reflection and refraction, but couldn’t explain others.
In the following centuries, light began to be thought of as a WAVE.

3. Huygen’s Principle Christian Huygens – Dutch mathematician/scientist
Described light waves spreading out from a point source as the overlapping of tiny secondary wavelets.

4. Saw this with Ripple Tank
Wide opening in barrier
Wave goes right through,
Bending around corners
With narrow opening,
More pronounced bending

5. On Ripple Tank, we saw Diffraction and Interference
Diffraction – bending of wave by anything other than reflection or refraction
Interference – overlapping of waves, producing areas of constructive and destructive interference.

6. Interference Patterns
We saw that increasing the frequency  longer wavelength, wider pattern
We saw that bringing sources together  wider also

7. Do we see these things with light?
Diffraction – laser on razor blade edge
Light bends around edges

8. Send light through tiny slit
Do we see interference pattern?
What happens if we narrow the slit width?

11. Patterns Different wavelengths of light produce different patterns.
Longer wavelengths, wider pattern.
(So red wider pattern than green)

12. White Light Separates
Send white light through diffraction grating, get separation of colors according to wavelength.

13. Compact Discs/DVDs
The tracks of a CD or DVD act as a diffraction grating, producing a separation of the colors of white light.
Opals, too!

14. Doppler Effect with Light
Like with sound waves, if a light source is moving towards an observer, they would experience a higher frequency (shift to blue end of spectrum)
Likewise, a light source moving AWAY would be shifted to red end of spectrum.

15. Red Shift of Stars
The fact that light from ALL distant stars and galaxies is red-shifted is convincing evidence that the universe is expanding.

16. Evidence that Light is a WAVE
Light shows diffraction
Light shows interference patterns
Light shows Doppler effect
Huygens, Young experiments
Maxwell’s Theory (electromagnetic wave theory)