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∆λ
∆
∆
=−
λλ
f
f
c
f
2
where
f = c
/
λ
is used. The negative sign means that an increase
in frequency corresponds
to a decrease in wavelength. We may interpret
∆
f
as the range of frequencies that can be
resolved and take it to be positive. Then,
2
c
f
Nm
∆=
and
∆
f
c
Nm
=
λ
.
(b) The difference in travel time for waves traveling along the two extreme rays is
∆
t =
∆
L
/
c
, where
∆
L
is the difference in path length. The waves originate at slits that are
separated by (
N
– 1)
d
, where
d
is the slit separation and
N
is the number of slits, so the
path difference is
∆
L
= (
N
– 1)
d
sin
θ
and the time difference is
∆
t
Nd
c
=
−
1
bg
sin
.
If
N
is large, this may be approximated by
∆
t =
(
Nd
/
c
) sin
. The lens does not affect the
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 Spring '08
 Any
 Physics, Power

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