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In a double-slit experiment, fringes are...

In a double-slit experiment, fringes are produced using light of wavelength `4800A^(@)`. One slit is covered by a thin plate of glass of refractive index 1.4 and the other slit by another plate of glass of same thickness and of refractive index 1.7. On doing so, the central bright fringe shifts to a position originally occupied by the fifth bright fringe from the centre. find the thickness of the glass plates.

Text Solution

Verified by Experts

The correct Answer is:
`2.4mum` and `4.8mum`
Shifting of fringe pattern due to plate is given by
`(D)/(d)(mu-1)`t [towards the side of plate]
due to two plates introducing infront of slits then shifting is result of both
`(D)/(d)[(1.7-1)2t-(1.4-1)t]=(5lamdaD)/(d)`
(Position of 5th bright fringe)
`(t-` thickness of one plate)
`t=5lamda=5xx4800Å=2.4mum`
`therefore` thickness of second `=2t=4.8mum`
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