Answer:

To calculate the refractive index of a substance, we can use the formula:

n = (c / v) * (1 + (F/D)), where n is the refractive index, c is the speed of light in a vacuum, v is the velocity of light in the substance, F is the focal length of the lens, and D is the distance of the object from the lens.

Given, the distance of the object is 20 point and the refractive index is 1.5

F = 1/((1/20) + (1/F))

Substitute the values and solve for F

F = 1/((1/20) + (1/F))

F = 1/((1/20) + (1/1.5F))

Solving for F

F = 40/3

Hence the focal length of the lens is 40/3 point

To find the curvature radius (R)

1/F = 1/R - 1/D

Substituting the values

1/F = 1/R - 1/20

Solving for R

R = (1/F) + (1/20)

R = (3/40) + (1/20)

R = 3/12

Hence the curvature radius of the lens is 3/12 point

To find the vertex distance (V)

1/F = 1/R - 1/D

Substituting the values

1/F = 1/R - 1/20

Solving for V

V = 1/F - R

V = (3/40) - (3/12)

V = 9/120

Hence the vertex distance of the lens is 9/120 point

To find the power of the lens

P = 1/F

Substituting the values

P = 1/F

P = 1/(40/3)

P = 3/40

Hence the power of the lens is 3/40

And the curvature radius, vertex distance, and power of the lens are 3/12 point, 9/120 point and 3/40 respectively.