Question

For a normal eye, the near point is 25.0 cm. This is where you would like to place printed material such as the newspaper to read. The far point is very far away. (a) What type and focal length corrective contact lens should a nearsighted person whose far point is 80.0 cm wear? What is the power of this lens? (b) What type and focal length corrective contact lens should a should a farsighted person wear if the person's near point is 60.0 cm away? What is the power of this lens?

Answer 1

Answer:

power is - 1.25 D

focal length is 0.429 m

power is 2.33 D

Explanation:

given data

near point  = 25.0 cm

far point  q = 80.0 cm

to find out

What type and focal length  for far point = 80.0 cm and near point = 60.0 cm away

solution

we apply here lens formula for concave lens

1/f = 1/p + 1/q

here we know p is infinity because near sight and q is negative i.e -80

1/f = 0 - 1/80

f = -80 cm

and power = 1/f

power = 1/80 = 0.0125 $cm^{-1}$

power = - 1.25 D

and

for far sight convex lens formula use

1/f = 1/p + 1/q

here p is 25 and q = -60

so 1/f = 1/25 - 1/60

1/f =  0.02333 $cm^{-1}$

f = 42.863 cm = 0.429 m

power = 1/f = 2.33 D