In an interference pattern the (n+4)th blue bright fringe and nth red bright fringe are formed at the same spot. If red and blue light have the wavelength of 7800Å and 5200Å, then value of n should be :
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Solution
Fringes are formed at same spot means fringes coincide n1λ1=n2λ2 (n+4)5200Å=(n)7800Å (n+4)4=6n n=8