Consider two palne convex lanse of same radius of curvature and refrective index `n_(1)` and `n_(2)` respectively. Now consider two cases :

Case - I : When `n_(1) = n_(2)=n`, then equivalent focal length of length is `f_(0)`
Case - II : When `n_(1) = n, n_(2) = n+ Delta n`, then equilivant focal length of lens is `f = f_(0) + Delta f_(0)`
Then correct options are :

Options

A. `|(Deltaf)/(f)| lt |(Deltan)/(n)|`
B. For `n=1.5, Deltan =10^(-3)` and f=20 cm, the value of `|Deltaf|` will be 0.02 cm (round off to `2^(nd)` decimal place).
C. If `(Deltan)/(n) lt 0` then `(Deltaf)/(f) gt 0`
D. The relation between `(Deltaf)/(f) and (Deltan)/(n)` remains unchanged if both the convex surfaces are replaced by concave surfaces of the same radius of curvature.