Question

What happens to the focal length of a
convex lens when it is kept in water ?
he
ark
ane.
Hence, after. meramani​

Answer 1

Answer:

We can find the answer from lens maker’s formula.

Let n

1

be absolute refractive index of material of glass and

n

2

be absolute refractive index of water.

The refractive index of thin lens in air is given by

f

a

1

=

R

1

1

–

R

2

1

n

1

−1

..................(1)

where R

1

andR

2

are radii of curvature of two surfaces of the convex lens.

Now, when lens is kept in water ,

we have to use refractive index of material of lens relative to water.

This is

n2

n1

So,replacing in the above expression n

1

by

n

2

n

1

, we get

f

w

1

=(

n2

n1

−1)(

R

1

1

−

R

2

1

)………………(2)

Comparison of Eq.(1) with Eq.(2) shows thatf

w

>f

a

Focal length increases.

Answer 2

Answer:

Hey ask the question properly