1. ) Focal length of the plano-convex lens is ............. when its radius of curvature of the surface is R and n is the refractive index of the lens.     [ ]

    2. a) f = R      b) f = R/2      c) f = R/(n–1)     d) f = (n–1)/R

  2. The value of the focal length of the lens is equal to the value of the image distance when the rays are      [ ]

    3. a) passing through the optic centre     b) parallel to the principal axis     c) passing through the focus      d) in all the cases

  3. ) Which of the following is the lens maker’s formula     [ ]

    a) 1/f = (n-1)(1/R1+1/R2)     b) 1/f = (n+1)(1/R1-1/R2)     c) 1/f = (n-1)(1/R1-1/R2)    

Suggested Experiments

  1. Conduct an experiment to find out the focal length of the lens.

  2. Let us assume a system that consists of two lenses with focal length f1 and f2 respectively.

    How do you find the focal length of the system experimentally, when

    i) two lenses are touching each other

    ii) they are separated by a distance ‘d’ with common principal axi




page no:80

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