If the distance between the first and the tenth minima of a double-slit pattern is 18 mm and the slits are separated by 0.15 mm with the screen 50 cm from the slits, we have to find the wavelength of the lights used.
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Solution: Click For PDF Version I n
a double-slit experiment the condition for interference minima is
where y is the distance of interference minima measured from the centre of the screen, as shown in the figure, and D is the distance of the screen from the slits. We note that the first and the tenth minima satisfy the following conditions:
We are given that
Therefore,
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We
assume that the angle
is small, and approximate
and
