PASCO OS-8500 INTRODUCTORY OPTICS SYSTEM - Manual (Page 69)

012-02744K Introductory Optics System
®
63
Exp 16: Single-Slit Diffraction
Suggestions on – Procedure
➀
The spacing between fringes increases with de-
creasing slit width.
➁
The double-slit patterns are a superposition of a
single-slit pattern and a “bar” pattern. The single-
slit pattern goes like this:
and the double-slit pattern shows this same intensity
pattern superimposed on a finer pattern.
The wavelengths obtained by this method are consis-
tently higher than expected. This is due to difficulties
in measuring the exact position of the minimum, due
to the width of that minimum. For a better way of
calculating wavelengths, use experiment 15.
➂
You would only see one maxima.
W sin tan
±1 X
L
= n
λ
sin tan
±1 X
L
=
λ
n
W
but if W <
λ then
λ
n
W
> 1 (unless n = 0)
However, sin(x) - 1; so the equation is not valid
unless n = 0. Therefore you would expect to see
only the zeroth maxima.
W = 0.04
L = 448
n X wavelength
Red 1 9 803.4E—9
2 18 802.9E—9
3 27 802.1E—9
Green 1 8 714.1E—9
2 16 713.8E—9
3 24 713.2E—9
Blue 1 7 624.9E—9
2 14 624.6E—9
3 22 653.9E—9
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-7 -5 -3 -1 1 3 5 7
Intensity
Position
Single-Slit Intensity
XX XX XX XX XX XX XX XX XXXXXXXXXXX XX X X X X X X X X X X X XX XXXXXXXX X X X X
X X
X
X
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X X X X XX XXX X X X
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X X X XXXX X X X
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X X X XXX X X X
X
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X X X XXXX X X X
X
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X X X XX XXXXXX XX X X X X X X X X X X X XX XX XXX XXXXXXXX XX XX XX XX XX XX XX X
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-7 -5 -3 -1 1 3 5 7
Intensity
Position
Double-Slit Intensity