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Will the focal length of a lens for red ...

Will the focal length of a lens for red light be more, sam or less than that for blue light

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If focal length of a given lens is f in air the accoding to lens maker formula,
`1/f = (mu -1 ) [ (1)/(R_1) - (1)/(R_2)]`
`therefore 1/f prop (mu -1)`
`( because` remaining terms remain constans
`rArr` We know that `mu_b gt u_r` and so `f_b lt f_r`
Thus, focal length of a given lens is smaller for blue light as compared to red light.
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