A point object is placed on the central axis in front of a c

A point object is placed on the central axis in front of a convex refracting surface with radius of 12 cm. Light is incident in air (n = 1) and refracted into a medium with n = 2. If the refracted rays are parallel to the central axis, what is the distance between the point and the refracting surface?

Solution

Use equation,

n1/p + n2/i = (n2-n1)/r

Where n2= refractive index of the convex refracting surface

n1 =  refractive index of the air

P= distance between the point and the refracting surface

i = distance between the image and the refracting surface

r = radius of refracting surface

n1/p + n2/i = (n2-n1)/r

Since the refracted rays are parallel to the central axis , i = infinity

1/p + 2/infinity  = (2-1)/0.12    =>  p = 0.12 m = 12cm