A thin equiconvex glass lens of refractive index 1.5 has power of 5D.When the lens is immersed in a liquid of refractive index "s" it acts as divergent lens of focal length 10ocm. the value if "s" is??
According to Lensmaker’s formula, the focal length for a convex lens placed in air can be obtained as
1/f = [(n2/n1) – 1] (1/R1 – 1/R2) where P = 1/f =5 and n2 = 1.5, n1=1
Therefore 5= (1.5 -1) (1/R1 – 1/R2) = 0.5(1/R1 – 1/R2)
1/f s= [(n2/ns) – 1] (1/R1 – 1/R2) where P = 1/fs =1/1m =1 and n2 = 1.5, n1=s
Taking ratio of the above two equation and simplifying ,
s = 1.67