Question

The radii of curvature of a double convex lens are 15
cm and 30 cm and its refractive index is 1.5. Calculate
its focal length.
[20 cm]​

Answer 1

Answer:

we know that the formula

1/f = R.I(-1)(1/R1-1/R2)

= 1.5(-1)(1/15-1/30)  ,     =-1.5(1/30)

=      1/f=  -1/20 ,     f=-20

hence, focal length=20cm.