1. Light
Wave nature of light

2. Is light what we see? Is there light where there is no one to see it?

3. Dualism of light
Isaac Newton believe light to be a ray of corpuscles (particles)
Robert Hooke believed light to have the wave-like nature
Newton won… until over a century after his death…

4. LIGHT INTERFERES!
1801 – Thomas Young produces interference of light

5. Light is a chameleon of science
Particles which interfere like waves?
A wave that travels in straight lines

6. Three views on light Waves Light rays Photons Most common
Visible light – part of EM spectrum
Interference and diffraction of light
Light travels in straight lines
Optics: mirrors, lenses, etc.
Photoelectric effect
Photons as particles (quanta of energy)
Quantum mechanics:
Not so much
Covered in HS physics

7. Waves or not?
Waves diffract (like sound). Light doesn’t seem to

8. Waves or not? Light does diffract when it goes through a tiny slit
When the opening is comparable to the wavelength, shadows are cast

9. Young’s Experiment

10. Constructive and destructive interference

11. Constructive and destructive interference
The waves coming from the slits interfere constructively or
destructively, depending on the difference in distances between
the slits and the screen.

13. Example
Red light (664 nm) is used in Young’s experiment with slits separated
by m. The screen is located a distance 2.75 m from the slits.
Find the distance on the screen between the central bright fringe and
the third-order bright fringe.

14. Formula for ‘bright spots’
Providing the screen is very-very distant,
Guess: what would the formula look like for dark spots?

15. Measuring wavelength of light
A double-slit interference pattern is observed on a screen 1.0 m behind two slits spaced 0.30 mm apart. The distance from the center of one particular fringe to the center on the ninth bright fringe from this one is 1.6 cm. What is the wavelength of the light?

16. Double-slit interference pictures

18. Single-slit diffraction

19. Huygens’ Principle

20. Diffraction
The wavelets going straight forward all travel the same distance to the screen. Thus they arrive in phase and interfere constructively to produce the central maximum
Note the brightness (intensity)!

21. Dark spots
Ray 2 is a/2 away from ray 1. If the two rays arrive counter-phase (trough / crest), destructive interference occurs. Ray 2 travels a longer distance by
Destructive interference will occur if:

22. Dark spots Position of destructive interferences (dark spots)
Note that p is not 0! That would be the central bright stripe
How wide would the stripe be?

23. How does the picture change??

24. Grating Diffraction

25. Sometimes More IS More