Question

Define focal length of the lens and calculate the focal length of the lens having radius of curvature 30cm

Answer 1

the point w]on principal axis where all the parallel rays to the principal axis after refraction meet at is called focus.the distance from pole to the focus is called focal length.

we know,

2f=c

f=c/2

f=30/2

f=15

Answer 2

The distance between the focus and the optical centre of a lens is known as focal length of the lens.

Radius=30

As we know ,

Radius is twice of focal length.

Therefore,

focal length(F) = 30÷2

=15

Hence focal length is 15 cm.