A person cannot read books placed nearer than 50"cm" from their eyes. What type of lens should they use to correct this?

1 Answer
Morgan
May 13, 2017

A convex lens should be used.

Explanation:

The person cannot read books placed nearer than 50 cm from their eyes. That means that 50 cm is the person's near point: the closest distance at which they can see something clearly. This distance recedes with age (i.e. assuming no need for vision correction, a 10-year old has a closer near point than a 40-year old).

This person is therefore considered to be farsighted. For a farsighted person, the object's image is formed behind the retina rather than on it, and as a result, they have difficultly observing near objects. To correct farsightedness (hyperopia), a convex lens is used to focus the image onto the retina.

The human eye as a lens:

Pearson Prentice Hall, Inc.

Some defects in vision:

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Near point:

Pearson Prentice Hall, Inc.

Correcting farsightedness:

Pearson Prentice Hall, Inc.

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