Question

A double convex lens is made up of glass of refractive index 1.55,with bot faces of the same radius of curvature . Find the radius of curvature required if focal length is 20 cm.

Answer 1

Ohkay...! Here's your answer....!

Rμ=1.55R1=RandR2=−Rf=20cmμ=1.55R1=RandR2=−Rf=20cm1f=(μ−1)[1R1−1R2]1f=(μ−1)[1R1−1R2]=> 120120=(1.55−1)(1R+1R)=(1.55−1)(1R+1R)=1.10R=1.10RR= 20×1.1= 22cmR= 20×1.1 = 22cmAnswer : 22cm
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Answer 2

Hey !!

1/f = [ μ₂ - μ₁  - ] [1/R₁ - 1/R₂]

   = 1/20 = [ μ₂ - μ₁ ] 2/R

   = R = (20 × 1.10) cm

   = -22 cm

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