Question

A concave mirror has a focal length of 20 cm. The distance between the two positions of the object for which the image size is double of the object size is 

Solution

Correct option is

20 cm

 

For real image:

            

For virtual image:

             

   

or       u2 = 10 cm  

Therefore, distance between two positions of the object are u1 – u2 or 30cm – 10cm = 20cm

SIMILAR QUESTIONS

Q1

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  

Q2

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    

Q3

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

                                                                

Q4

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? 

Q5

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,

                                           

Q6

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  

 

Q7

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  

Q8

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

                                                                     

Q9

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

Q10

A plane mirror is placed at origin parallel to y-axis, facing the positive x-axis. An object starts from (2m, 0, 0) with a velocity of . The relative velocity of the image with respect to the object is along