Question

A thin convex lens is made with glass of refrective index 1.5 and it's focal length is 0.2m if it is acts as a concave lens of focal length 0.5m when dipped in a liquid then the refractive index of the liquid is a.17/8 b. 15/8 c.13/8. d. 9/8​

Answer 1

Answer:

15/8

μ

1

=1.5

f

1

=0.2m

f

2

=(−0.5)

μ

2

=?

Using lens makers formula and taking ratios,

f

2

f

1

=

(μ

1

−1)

(μ

2

−1)

⇒

(−0.5)

0.2

=

(1.5−1)

(

μ

e

1.5

−1)

⇒

0.5

0.2×0.5

=(1−

μ

e

1.5

)

⇒

μ

e

1.5

=0.8

⇒μ

e

=

8

15

Answer 2

Answer:

Given,

μ

1

=1.5

f

1

=0.2m

f

2

=(−0.5)

μ

2

=?

Using lens makers formula and taking ratios,

f

2

f

1

=

(μ

1

−1)

(μ

2

−1)

⇒

(−0.5)

0.2

=

(1.5−1)

(

μ

e

1.5

−1)

⇒

0.5

0.2×0.5

=(1−

μ

e

1.5

)

⇒

μ

e

1.5

=0.8

⇒μ

e

=

8

15