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 2 
10 8 m/sec , the focal length of the lens is
Text Solution
Verified by ExpertsThe correct answer is:
C
According to lens formula 
The lens is plano-convex i.e ., 
and 
Hence 
Speed of light in medium of lens 
⇒ ⇒ 
If r is the radius and y is the thickness of lens (at the centre), the radius of curvature R of its curved surface in accordance with the figure is given by
Neglecting 
we get 
cm
Hence 
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