Question

The plane face of a plano-convex lens is silvered. If μ be the refractive index and R, the radius of curvature of curved surface, then the system will behave like a concave mirror of radius of curvature:

Solution

Correct option is

 

When an object is placed in front of such a lens, the rays are first of all refracted from the convex surface, then reflected from the polished plane surface and again refracted from convex surface. If fl and fm be the focal lengths of lens (convex surface) and mirror (plane polished surface) respectively, then effective focal length is

                 

  

   

SIMILAR QUESTIONS

Q1

A luminous object is placed at a distance of 30 cm from a convex lens of focal length 20 cm. On the other side of the lens, at what distance from the lens must a convex mirror of radius of curvature 10 cm be placed in order to have an upright image of the object coincident with it

Q2

The far-point of a short-sighted eye is 200 cm. The power of the lens is:

Q3

The near point of a short-sighted person is 10 cm and he desires to read a book 30 cm away from him. The power of the lens to be used by him is:

Q4

The distance between an object and the screen is 100 cm. A lens produces an image on the screen when placed at either of the positions 40 cm apart. The power of the lens is: 

Q5

A thin equiconvex lens has focal length 10 cm and refractive index 1.5. One of its faces is now silvered and for an object placed at a distance u in front of the lens, the image coincides with the object. The value of u is:

Q6

The plane face of a plano-convex lens of focal length 20 cm is silvered. What type of mirror will it become and of what focal length 

Q7

A convex lens of focal length 20 cm is cut into two equal parts so as to obtain two plano-convex lenses as shown in figure. The two parts are then put in contact as shown in figure. What is the focal length of the combination?

                                                                       

Q8

As shown in figure, a convergent lens is placed inside a cell filled with liquid. The lens has focal length +20cm when in air, and its material has refractive index 1.50. If the liquid has refractive index 1.60, the focal length of the system is: 

                                                                                     

Q9

A plano-convex lens of f = 20 cm is silvered at plane surface. Now, f will be (μ = 1.5): 

Q10

A convex lens of focal length f is placed somewhere in between an object and a screen. The distance between the object and the screen is x. If the numerical value of the magnification produced by the lens is m, the focal length of the lens is: