Four combinations of two thin lenses are given in List `I`. The radius of curvature of all curved surfaces is `r` and the refractive index of all the lenses is `1.5` Match lens combinations in List `I` with their focal length in List `II` and select the correct answer using the code given below the lists.
(A) `(p) 2 r`
(B) `(q) ( r)/(2)`
( C) `(r) - r`
(D) `(s) r`.
Code :

Options

A. P-1 , Q-2 , R-3 , S-4
B. P-2 , Q-4 , R-3, S-1
C. P-4 , Q-1, R-2 , S-3
D. P-2 , Q-1, R-3 , S-4

Answer

B

Explanation

`P rarr 2 `
`(1)/(F_("eq")) = (1)/(f_(1)) + (1)/(f_(2)) = (1.5 - 1) ((2)/(r))xx 2 = (2)/(r)`
`F_("eq") = r//2`

`Q rarr 4`
`(1)/(F_("eq")) = (1.5 - 1) ((2)/(r)) = (1)/(r)`
`F_("eq) = r`

`R rarr 3 `
`(1)/(F_("eq)) = (1.5 -1) ((-2)/(r)) = -(1)/(r)`