334
CHAPTER 24
24.68
Phase reversals occur in the reflections at both surfaces of the oil layer, so there is zero
net phase difference due to reflections. The condition for constructive interference is
then
2
bright
n
film
tm
m
n
λ
==
(1)
and the condition for destructive interference is
11
2
22
dark
n
film
m
n
=+
(2)
Solving for the order number,
m
, in equation (1),
and substituting into equation (2) gives the film thickness as
()
500 nm
313 nm
4 1.20
1
500 nm 750 nm
41
dark
film
dark
bright
t
n
λλ
=
−
−
24.69
(a) Assuming that
n
in the figure at the
right, Ray 1 undergoes a phase reversal as it
reflects at point A, but Ray 2 has no reversal
as it reflects at B. Therefore, the condition for
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 Spring '09
 Physics, Work, optical path lengths

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