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Interference
- If light is a wave, it should exhibit wave-like phenomena such as interference and
diffraction
when several conditions are met.
- Monochromatic Light
- Coherent Light
- one source becomes two by using two slits as the two sources.
- wavelength of light is small, need small slits (without diffraction
this will not work)
Superposition
- light is composed of electric and magnetic
fields which obey superposition.
- Constructive Interference
- path difference = full wavelength
- Destructive Interference
- path difference = odd integer half-
wavelength
- Geometry
- screen-slit distance = L
- slit separation = d
- If L >> d
- rays are approximately parallel and the path difference between
the two rays is d sinq
- Constructive Interference
- path difference = full wavelength
- dsinq = ml
- small angle approximation
- sinq is about equal to tanq = y/L
- y = ml L/d (bright spots)
- Destructive Interference
- path difference = odd integer half- wavelength
- dsinq = (m + 1/2)l
- Intensity
- Thin Film Interference
- "Rainbow of Colors"
- Soap Bubbles
- Oil Slicks
- thickness determines which colors strongly reflected
- varying thickness means different colors will be reflected
- light reflecting at second boundary
travels
greater distance
- the light is incident perpendicular to the surface. It is drawn at an angle so that we can distinguish between the incoming and outgoing light.
- 2t
- but the wavelength also
changes
- 2nt
- may undergo phase shift
- Constructive
- Destructive