1)

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

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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:

Option B

Explanation:

(P)  1r=(321)(1r+1r)=1r

          f=r

                      1feq=1f+1f=2r

                feq=\frac{r}{2}$

    

(Q)   1r=(321)(1r)f=2r

                     1f+1f=2f=1r

                      feq=r

(R)     1f=(321)(1r)12r

                          f=-2r

          

           1feq=1f+1f=22r

    

    feq=-r

 

(S)          

           1feq=1r+12r=12r

           feq=2r