Question

a plano convex lens of radius of curvature 10cm.Its focal length is 80 cm under water.Calculate the refractive index of the material of the lens given refractive index of water is 4/3​

Answer 1

Answer:R1 = 10 cm; R2 = ∞; f = 80 cm and μwater = 43

So, Focal length of the plano - convex lens, when it is immersed in water is,

1fw = (μrel−1)[1R1−1R2] ⇒ 180 = (μmμwater−1)[110−1∞] ⇒ 180 = (μm43/−1)[110] ⇒ 18 = (3μm4−1) ⇒ 3μm4 = 98⇒ μm = 32

Therefore, refractive index of the material is 1.5

Explanation: