NEET Physics Ray Optics and Optical Instruments Questions Solved


There  is an equiconvex glass lens with radius of each face as R and  and . If there is water in object space and air in image space, then the focal length is

(a)   2R                                      (b)   R

(c)   3 R/2                                  (d)  R2

     

(c) Consider the refraction of the first surface i.e. refraction from rarer medium to denser medium

      μ2-μ1R=μ1u+μ2v132-43R=43+32v1v1=9R           

  Now consider the refraction at the second surface of the lens i.e. refraction from denser medium to rarer medium

                  

   1-32-R=-329R+1v2v2=32R            

    The image will be formed at a distance of 32R. This is equal to the focal length of the lens.

Difficulty Level:

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