Question

Equiconvex lens are to be manufactured from refractive index 1.5. What will be the radius of curvature if the lens should have a focal length of 20 cm?​

Answer 1

Answer:

The focal length of a thick lens is given by the Lens' Maker Formula-

f

1

=(μ−1)(

R

1

1

−

R

2

1

+

μR

1

R

2

(μ−1)d

)

=(1.5−1)(

+20

1

−

−20

1

+

1.5(20)(20)

0.5(5)

)

⟹f=19.2cm

Hence the image of object far from lens is formed at its focus, that is, at a distance 19.2cm.