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WAVE NATURE OF LIGHT Light. Is light what we see? Is there light where there is no one to see it?

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Presentation on theme: "WAVE NATURE OF LIGHT Light. Is light what we see? Is there light where there is no one to see it?"— Presentation transcript:

1 WAVE NATURE OF LIGHT 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 A wave that travels in straight lines Particles which interfere like waves?

6 Three views on light WavesLight raysPhotons 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: Covered in HS physics Not so much

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

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

9 Young’s Experiment

10 Constructive and destructive interference

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

12

13 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. Example

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

17

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?? bcs/Books?action=mininav&bcsId=4678&i temId= &assetId=160341&reso urceId=15300

24 Grating Diffraction

25 Sometimes More IS More


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