Question

The refractive index of glass with respect to air is 3/2
and that of water is 4/3. The radii of curvature of a
glass convex lens are 20 cm and 30 cm respectively
,
What will be the focal length of the lens (i) in air
(ii) in water?​​

Answer 1

Answer:

From lens maker's formula,

f

1

=(μ−1)(

R

1

1

−

R

2

1

)

We have,

Refractive index, μ=1.5 and R

1

=20 cm and R

2

=30 cm

f

1

=(1.5−1)(

R

1

1

−

R

2

1

)

f

1

=(1.5−1)(

−20

1

−

−30

1

)

f

1

=(1.5−1)

20×30

−30+20

f=−120cm