1.

A biconvex lens has a focal length 2/3 times the radius of curvature of either surface. Calculate the refractive index of lens material.

Answer»

Solution :It is given that for a BICONVEX lens `|R_(1)| = |R_(2)| = R` (SAY) and focal length of lens `|f| =2/3 R`
APPLYING lens maker.s formula `1/f = (n-1) (1/R_(1) -1/R_(2))`, we get
`1/(+2/3R) = (n-1) [1/(+R) -1/(-R)]` or `3/(2R) = (n-1) 2/R rArr n= 7/4 = 1.75`


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