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

Answer

A, C, D