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Single Slit Diffraction
A ray passing through the center of the slit will have a path length exactly
λ
/2 greater than that
from the source at
A
, and hence these two waves will interfere destructively. Now consider a
point adjacent to
A
; the light emitted with have a path difference exactly
λ
/2 different to light
from a point just above the central point, and will cancel it out. Similarly, for every point
between
A
and the center, there will be a corresponding point
λ
/2 away between the center and
B
that will destructively interfere with it. Hence there is effectively no light emitted it the direction
θ
m
and it corresponds to a minimum. A similar situation arises when the path difference between
A
and
B
is any whole number of wavelengthssuch a situation is shown in , iv). On the other
hand, when the path difference between
A
and
B
is a halfinteger multiple of the wavelength,
such as in iii), there will only be partial cancellation. All the emitters between
A
and a point one
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 Fall '10
 DavidJudd
 Physics, Diffraction, Light

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