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Introduction
VIDEO
...introduction to the
Interference Patterns
produced by the
Diffraction of light
through small gaps.

Page 3

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Introduction
In DIFFRACTION, only
the direction of wave
travel (ray) is changed
when the wave passes
through an opening.
The effect is most
noticeable when the
opening size

Page 4

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Introduction
DIFFRACTION can only
be produced by waves.
So ELECTRON
DIFFRACTION is key
evidence that particles
are waves. (See Wave
Particle Duality)

Page 5

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Uses
Diffraction is a key
method for creating
INTERFERENCE
PATTERNS; diffracted,
coherent waves
superpose to give
regions of constructive
and destructive
interference (due to the
path difference between
the waves)

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Coherence
"Coherent" sources
produce waves which
have:
1. The same wavelength

2. The same phase

relationship.
3. Similar amplitudes

Page 7

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Path and
Phase
Try not to confuse Path
Difference and Phase
Difference.
Path difference is a
distance expressed in
metres (or some
multiple of , e.g. 3/2)
Phase difference is the
same thing expressed
as an angle

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Conditions
To get constructive
interference at a point,
the path difference
between any waves
arriving at that point
must equal n. Where n
is equal to 0, 1, 2, 3,
etc

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Maxima
Since the amplitude of
the resultant wave at a
point of constructive
interference is a
maximum, these
positions are also
known as Maxima.

Page 10

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Conditions
To get destructive
interference, the path
difference between any
waves arriving at these
point must equal
(n+½).
Again, n is equal to 0,
1, 2, 3, etc

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