SingleAperture Interference
When coherent light shines through a single small slit onto a screen, the multiple slit
diffraction equation (
2
l
sin
θ
= N
λ
) fails to predict the maxima and minima. The first
problem is that
l
was used to describe the distance between the slits, but now there is only
one. Next, the central bright fringe is roughly three times wider
than all the other maxima, which drop off in intensity very
rapidly as shown. Clearly, the light is undergoing interference,
but some adjustments will be needed if a simple equation is
still going to be used to describe it.
The solution is to use exactly the same equation with three
critical concessions: First,
l
now describes the width of the slit
itself. Second,
odd
values of
N
now describe maxima and
even
values describe minima.
(This may be easier to remember if one bears in mind that a
single
slit is an odd number,
even though this implies that all numbers greater than one are even.) Third,
zero
will no
longer be allowed as a valid number. That is, the entire central maximum will be
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This note was uploaded on 04/05/2012 for the course PHYS 131 taught by Professor Tibbets during the Spring '11 term at Cuyamaca College.
 Spring '11
 Tibbets
 Diffraction, Light

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