Question

A double convex lens has two surfaces of equal radii 'R’and refractive inder n=1.5, find the focal length ‘f”.
​

Answer 1

Answer:

Given

Radius of curvature =R

focal length =f

Refractive index, μ=1.5

From lens maker's formula

f

1

=(μ−1)[

R

1

1

−

R

2

1

]

f

1

=(1.5−1)[

R

1

+

R

1

]

=0.5×

R

2

f

1

=

R

1

f=R

Answer 2

Explanation:

In the case of a convex mirror, it is the point at which all rays parallel and close to the principal axis appear to diverge from after reflection. (See the figure above). It is also called the focal point. Focal plane- it is a plane perpendicular to the principal axis and passes through the focal point.