Question

A plano-convex lens when silvered on the plane side behaves like a concave mirror of focal length 60 cm. However, when silvered on the convex side, it behaves like a concave mirror of focal length 20cm. Then, the refractive index of the lens is  

 

Solution

Correct option is

1.5

 

    

               

                        

                  …(i)

                                  

  

Dividing (i) by (ii), we get 

                 

  

SIMILAR QUESTIONS

Q1

What should be the value of distance d so that final image is formed on the object itself. (Focal lengths of the lenses are written on the lenses). 

                                                  

Q2

A car fitted with a convex mirror of focal length 20 cm. A second car 2 m broad and 1.6 m high is 6 m away from the first car. The position of the second car as seen in the mirror of the first car is

Q3

In the above question, the breadth and height of the second car seen in the mirror of the first car are, respectively, 

Q4

In the above question, if the second car is overtaking at a relative speed of 314 ms–1, how fast will the image be moving? 

Q5

A ray of light passes from glass, having a refractive index of 1.6, to air. The angle of incidence for which the angle of refraction is twice the angle of incidence is  

Q6

Consider an equiconvex lens of radius of curvature R and focal length f. Iff > R, the refractive index μ of the material of the lens    

Q7

A fish is vertically below a flying bird moving vertically down toward water surface. The bird will appear to the fish to be 

                                                                

Q8

What is the angle of incidence for an equilateral prism of refractive index  so that the ray is parallel to the base inside the prism? 

Q9

A cube of side 2m is placed in front of a convex mirror of focal length 1 m with its face A at a distance of 3 m and face B at a distance of 5m form the mirror. The distance between the images of faces A and B and heights of images of A and B are, respectively,

                                           

Q10

Two thin lenses are placed 5 cm apart along the same axis and illuminated with a beam of light parallel to that axis. The first lens in the path of the beam is a converging lens of focal length 10 cm whereas the second is a diverging lens of focal length 5 cm. If the second lens is now moved toward the first, the emergent light