Question

5. “Due to Adarsh Gram Yojana in Maharashtra not only agriculture but also animal husband
by got well developed.” Comment.
6. What is the focal length of double concave lens kept in air with two spherical surfaces of
radii R1
= 30cm and R2
=60cm. Take refractive index of lens as n = 1.5.
7. How are fats digested in our bodies? Where does this process take place?
8. Where do we use MEAN in day to day life?

Answer 1

Thus the value of focal length is f = -30 cm

Explanation:

What is the focal length of double concave lens kept in air with two spherical surfaces of  radii R1  = 30 cm and R2  = 60 cm. Take refractive index of lens as n = 1.5

solution:

Given data:

• R₁ = - 20 cm  
• R₂ = + 60 cm

For refraction on the concave surface:

μ₂ / v₁ - μ₁ / u = (μ₂ - μ₁ ) / R₁

μ₁ / v - μ₂ / v₁ = - (μ₂ - μ₁)/R₂

1 / f = 1 / v - 1 / u

We get    1 / v - 1 / u = (μ₂₁ - 1) [1 / R₁  - 1 / R₂]

The equation is:  

1 / f = (μ₂₁ - 1)  [ 1 / R₁ - 1 / R₂ ]

1 / f = (1.5 - 1) x [ - 1 / 20 - 1 / 60] = - 1/30

f = -30 cm

Thus the value of focal length is f = -30 cm