Explain YDSE
Young's Double Slit Experiment (YDSE)
For an interference pattern to be observable,
Two sources are said to be coherent
if waves from the sources have a constant phase difference between them.
Young’s Double Slit Experiment A simple experiment of the interference of light was demonstrated by Thomas Young in 1801.
It provides solid evidence that light is a wave.
Interference fringes consisting of alternately bright and dark fringes (or bands) which are equally spaced are observed. These fringes are actually images of the slit.
At O, a point directly opposite the mid-point between S1 and S2, the path difference between waves is zero.
Thus constructive interference occurs and the central fringe or maxima is bright.
Suppose P is the position of the nth order bright fringe (or maxima). The path difference between the two sources S1 and S2 must differ by a whole number of wavelengths.
As the distance D is very much larger than a, the path difference can be approximated by dropping a perpendicular line S1 N from S1 to S2 P such that
and
the path difference
From geometry, S2N = a sin θ where a is the distance between the centres of the two slits.
Equating, a sin θ = nλ and re-arranging,
But from geometry,
where xn = distance of nth order fringe from the central axis Since θ is usually very small,
tan θ ≈ sin θ
i.e. or
Thus the separation between adjacent fringes (i.e. fringe separation) is,
Thus,
Fringe separation
Clearly Δx is a constant if λ, D and a are kept constant. If all factors are kept constant, the fringes are evenly spaced near the central axis.
various diagrams
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