Question

calculate the focal length of a Plano Convex lens for which the radius of curved surface is 25cm and relative index of the material of the lens is 1.5.

Answer 1

Answer:

For the double convex lens

f=25cm,R

1

=R and R

2

=−2R (sign convention)

f

1

=(μ−1)(

R

1

1

−

R

2

1

)

⇒

25

1

=(15−1)(

R

1

−

−2R

1

)=0.5(

2

3R

)

⇒

25

1

=

4

3

R

1

⇒R=18.75cm

R

1

=18.75cm,R

2

=2R=37.5cm