Question

If a farsighted person has a near point that is 0.600 mm from the eye, what is the focal length f2f2f_2 of the contact lenses that the person would need to be able to read a book held at 0.350 mm from the person's eye

Answer 1

Answer:

0.227mm

Explanation:

Since the person is long sighted, the eye defect can be corrected using a convex lens.

A convex lens has a positive focal length but its image distance is either positive or negative depending on image type since it can form both real and inverted image.

If the book is the image, the image distance from the lens will be 0.350mm and the object distance will be 0.650mm which is the near point of the person.

According to the lens formula;

1/f = 1/u+1/v where;

f is the focal length

u is the object distance = 0.350mm

v is the image distance = 0.650nm

1/f = 1/0.350+1/0.650

1/f = 2.86+1.54

1/f = 4.40

f = 1/4.40

f = 0.227mm

The focal length of the lens is 0.227mm

Note that it is safe to use image distance as positive since we are not told the nature of the image.