Question

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  

Solution

Correct option is

Changes from parallel to divergent

                                                    

 

At 5 cm from the lens, the second lens has a virtual object (image of the first lens) at its focal length. The emergent rays are therefore parallel.

                                                                 
When the second lens is closer than 5 cm to the fist lens, its object is outside the focal length of the diverging second lens. This produces a virtual image outside 2f of the second lens. The emergent rays are therefore divergent.   

SIMILAR QUESTIONS

Q1

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

Q2

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

Q3

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? 

Q4

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  

Q5

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    

Q6

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

                                                                

Q7

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? 

Q8

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,

                                           

Q9

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  

 

Q10

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