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SHAOUL EZEKIEL: Now we're ready
to look at two-slit diffraction

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patterns.

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What we have here is a slide.

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And on this slide, we
have pairs of slits.

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The individual width of
each slit is 100 microns,

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and the spacing between slits
varies anywhere from 150

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microns to 2 millimeters.

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The only thing we've added
to the previous setup

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is this lens in order
to expand the beam so

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that we can cover both slits.

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So let's first look at
the diffraction pattern

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associated with a single slit.

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Now, if we look at the
screen in close-up,

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you can see we have a
single-slit diffraction

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pattern.

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As before, the circles
are 5 centimeter markers.

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And in addition now, we've added
the little squares, the two

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squares.

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And that denotes the
separation between the 0s

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of the central lobe of the
single-slit diffraction

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pattern.

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Let me remind you that the
spacing between the slide

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here and the screen is
about 200 centimeters.

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And we're using
6,328 Angstrom light.

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So you have all the
tools needed, then,

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to calculate spacings
and what have you.

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So now, let's start by looking
at the smallest spacing, which

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is 150 microns.

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So indeed what you see is that
the single-slit diffraction

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pattern has been modified by
the addition of the other lobes,

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of the smaller lobes.

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And this is for
150 micron spacing.

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Remember, each slit
width is 100 microns.

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Now, let's go on
and look at 175.

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Well, 175 from 150 is
not much of a change.

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So we don't expect to see much
narrowing of the small lobes.

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Let's go on to 200.

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Here, you're beginning
to see that the lobes

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under the single-slit
diffraction pattern

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are now narrower.

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And now 300 micron
separation-- here it's clear.

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They're getting they're
getting narrower.

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In fact, you have
about five of them

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or so under the central lobe
of the single-slit diffraction

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pattern.

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Now let me go on to the 2,000,
or 2 millimeter spacing.

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And at first, you
think there's no little

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lobes under this single-slit
diffraction pattern.

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But all we have to do here
is get the camera to zoom in.

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And as it zooms in, you begin
to see that indeed, there

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is structure there.

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And if your calculations
are correct,

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you'll be able to show
what the spacing is

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for a 2-millimeter
slit separation.

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Now, in the next
demonstration, we're

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going to show the Frauenhofer
diffraction pattern associated

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with many slits.