Diameter Of A Plano-convex Lens Is 6 Cm And Thickness At The Centre Is 3 Mm. If The Speed Of Light In The Material Of The Lens Is , The Focal Length Of The Lens Is:  

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Question

Diameter of a plano-convex lens is 6 cm and thickness at the centre is 3 mm. If the speed of light in the material of the lens is , the focal length of the lens is:  

Solution

Correct option is

30 cm

 

  

   

As the lens is plano-convex, i.e., R1 = R and R2 = ∞,   

  

As speed of light in the medium of lens is   

                  

 From figure,   

                

  

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