Question

Calculate the focal length of a convex lens whose radii of curvature of two surfaces is 10 cm and 15 cm respectively and its refractive index is 1.5. 

Answer 1

Given : 

`f = ?`  `R_1 =10  "cm"`    `R_2 = 15  "cm"`  `mu = 1.5`

`1/f = (mu - 1)(1/R_1 - 1/R_2)`

`1/f = (1.5 - 1)(1/10 - 1/15)`

`1/f = (0.5)(0.1 - 0.066)`

= `(0.5)(0.034)`

`1/f = 0.017``

`therefore f = 58.82  "cm"`