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Unformatted text preview: c) Paths A and B also travel different distances before reaching the observer. How much extra, distance
does path B travel, and how many extra cycles of phase shift does this result in? (Be careful with the
wavelength of the Eight!) cl) What type of interference does the observer see between beams A and B: constructive, destructive, or
neither? Briefly explain your answer. \ e) How would your answers to parts (a) through (d) change if, instead of using blue light, we used red light 1
i with a wavelength It, = 600 am? What does this explain about the way soap films look in real life? (Think ,
about how-actual soap films look before answering this last question — if your an%ter is “they look blue” or ‘
“they look red”_,mtlien you spend far too little time around soap films!) - (sﬁw’ i
i D All/hen the film is about to pop, it will often grow so thin that its thickness 2, is far smaller than the _ 7‘ __ _ __
wavelength of visible light of any color. In this case, what will you see if you observethe light reflected
from the film? Have you seen this happen in real life? ' ‘i
a I Physics 6B
Discussion Section Problem — Week of March 10 A soap film of thickness 2 = 225 nm is illuminated from the left by blue light with wavelength 1,, = 400 nm.
The film itself has refractive index 23;: 1.333, and is surrounded on both sides by air with index n = 1.000. A observer is stading to the left of the film, looking at the light reﬂected from the film. The two main ways
that light can reach the observer’s eyes are path A and path B, as shown above. a)“ - Light vvhicliwiravels along path A meets the interface between the air and the soap film only once, at point P. Does this light experience a half-cycle phase shift at this point? Brieﬂy explain why or why not. b) Light which travels along path B meets the interfaces-iiia‘jtix'epn the air and the soap film three times, at
points Q, R, and S. Does this light experience a half-cycie‘phase shift at any of these points? Briefly
explain why or why not. ...
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This homework help was uploaded on 04/16/2008 for the course PHYS 6B taught by Professor Graham during the Winter '08 term at UCSC.
- Winter '08