The focal length of a double convex lens is 20cm . The radii of curvature of the surface of this lens are 20 cm and 40 cm , respectively. Then, the refractive index of the material of the double convex lens is

Question

The focal length of a double convex lens is 20cm . The radii of curvature of the surface of this lens are 20 cm and 40 cm , respectively. Then, the refractive index of the material of the double convex lens is (A) (5/2) (B) (4/3) (C) (5/3) (D) (4/5)

Tardigrade Admin · Accepted Answer

Here, R1=20 cm R2==-40 cm, f=20 cm (1/20)=(μ - 1)((1/20) + (1/40));(1/20)=(.μ -1.)(3/40)⇒ μ =(5/3)

Q. The focal length of a double convex lens is $20 c m$ . The radii of curvature of the surface of this lens are $20 c m$ and $40 c m$ , respectively. Then, the refractive index of the material of the double convex lens is

$\frac{5}{2}$

$\frac{4}{3}$

$\frac{5}{3}$

$\frac{4}{5}$

Here, $R_{1} = 20 c m R_{2} == - 40 c m, f = 20 c m$
$\frac{1}{20} = (μ - 1) (\frac{1}{20} + \frac{1}{40}); \frac{1}{20} = (μ - 1) \frac{3}{40} \Rightarrow μ = \frac{5}{3}$

Q. The focal length of a double convex lens is 20cm . The radii of curvature of the surface of this lens are 20cm and 40cm , respectively. Then, the refractive index of the material of the double convex lens is

25​

34​

35​

54​