Q.

In a long glass tube, mixture of two liquids A and B with refractive indices 1.3 and 1.4 respectively, forms a convex refractive meniscus towards A. If an object placed at 13 cm from the vertex of the meniscus in A forms an image with a magnification of '–2' then the radius of curvature of meniscus is:          [2025]

1 1 cm  
2 13 cm  
3 23 cm  
4 43 cm  

Ans.

(3)

μA=1.3, μB=1.4 and u=13 cm

m=vμBuμA=2

 v=2u(μBμA)

            =2(13 cm)(1.41.3)=+28 cm

Also, μBvμAu=μBμAR

          1.4281.313=0.1R  R=23 cm