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 8 1 2 10 ms  , focal length of the lens is 1) 15 cm 2) 20 cm 3) 30 cm 4) 10 cm

Answer 1

Explanation:

n=c/v = 1.5

R ² -(R -0.3 )² = 3²

R² - R² + 0.6R +0.09 = 9

R = 15 cm

f = R /(n-1)

  = 15 / 0.5

   = 30 cm