12
THE DOUBLE SLIT
CAUTION: Do NOT look directly into a laser beam or even a reflected beam!!!!
Objective
Measure the wavelength of a laser beam by generating a twoslit interference pattern.
Theory
The wave nature of light accounts for the interference
observed when monochromatic light of wavelength
λ
is used to
illuminate a pair of slits with spacing
d
.
Rays 1 and 2 pass through
the two slits.
The rays interfere constructively when their path
length difference is an integer multiple of the wavelength.
Under these conditions,
d
sin
θ
=
m
λ
,
(1)
where
m
is an integer called the
order
of the interference maximum and
θ
is the angle which the
rays make relative to the incident beam direction.
The
m
th
maximum will occur at the angle
⎟
⎠
⎞
⎜
⎝
⎛
=
−
d
m
m
λ
θ
1
sin
.
(2)
If one observes an interference pattern and measures
θ
m
, these equations can be used to
measure
d
, if
λ
is known (or viceversa).
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 Spring '10
 AARONSUP
 Diffraction, Light, Wavelength, INTERFERENCE PATTERN

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