A lens forms a real image of an object. The distance from the object to the lens is x cm and that from the lens to the image is y cm. The graph (see fig) shows the variation of y with x.

It can be deduced that the lens is



Correct option is

Converting and of focal length 10 cm


A diverging lens is ruled out because both x and y are positive values. Bothx and y equal 20 cm at their smallest sum, which occurs when 

                    x + y = 40 cm = 4f   


This indicates a converging lens of focal length = 10 cm.  



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


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? 


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  


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    


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



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? 


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,



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  



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  


A point source S is placed at the bottom of different layers as shown in fig. The refractive index of the bottom-most layer is μ0. The refractive index of any other upper layer is 


A ray of light starts from the source S as shown. Total internal reflection takes place at the upper surface of layer having n equal to