A Thin Flat Glass Plate Is Placed In Front Of A Convex Mirror. At What Distance B From The Plate Should A Point Source Of Light S Be Placed So That Its Image Produced By The Rays Reflected From The Front Surface Of The Plate Coincides With The Image Formed By The Rays Reflected From The Mirror? The Focal Length Of The Mirror Is F = 20 Cm And The Distance From The Plate To The Mirror A = 5 Cm. How Can The Coincidence Of The Images Be Established By Direct Observation                                                                                                                                      

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Question

A thin flat glass plate is placed in front of a convex mirror. At what distance b from the plate should a point source of light S be placed so that its image produced by the rays reflected from the front surface of the plate coincides with the image formed by the rays reflected from the mirror? The focal length of the mirror is f = 20 cm and the distance from the plate to the mirror a = 5 cm. How can the coincidence of the images be established by direct observation

                                                                                                                                     

Solution

Correct option is

15 cm

 

mage formed by plane mirror = (– 15) cm         

Object distance from mirror = (b + 5) cm    

Now,  

         1/v  + 1/u =1/f

      

                     b = 15 cm.

 

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