A laser with wavelength of 639 nm is set up to shine through a Young's double-slit mask. A screen is positioned 1.1 m from the double slits. The distance between alternating bright bands on the screen is observed to be 0.81 cm. What is the distance between the slits? (1 nm = 10 9 m) O a. 7.5E-6 m Ob.1.2E-2 m O.4.7E-9 m O d.9.3E-5 m O . S.7E-5 m
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In Young's Double slit experiment a screen is placed at a certain distance apart from the slits. When the slits are illuminated with light from the source, alternate bright and dark bands appear on the screen, justifying the superposition of the light waves emerging from the slits. The formation of bright bands is because of constructive interference of light i.e. the position where crests of both waves meet while dark band is the position where destructive interference takes place i.e. where the crest i.e. minima of one wave coincide with the trough i.e. maxima of the other. All the bands are of equal width and the bands disappear as soon as one of the slits is covered. The essential condition for interference is that the light waves should be coherent, that means they should vibrate in same phase. That is why, the double slits are used because the two sources are derived from the same source.
Now distance between successive fringes is given as fringe width
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