Question

a) When glasses (or contact lenses) are usedto correct nearsightedness, where should the corrective lens forman image of an object located at infinity in order for the eye toform a clear image of that object?

The lensshould form the image at the near point. The lensshould form the image at the far point. The lensshould form the image at a point closer to the eye than the nearpoint. The lensshould form the image at a point farther from the eye than the farpoint.

c) When glasses (or contact lenses) are used to correctfarsightedness, where should the corrective lens form an image ofan object located between the eye and the near point in order forthe eye to form a clear image of that object?

The lensshould form the image at the near point. The lensshould form the image at the far point. The lensshould form the image at a point closer to the eye than the nearpoint. The lensshould form the image at a point farther from the eye than the farpoint.

Answer 1

Concepts and reason

The concepts used in this question are Myopia and Hypermetropia.

First, find the type of lens used to correct nearsightedness. Then, explain the formation of image by the lens in front of eye. Then, find the type of lens used to correct farsightedness. Then, explain the formation of image by the lens in front of eye. Finally, compare all the statements with the facts to find the correct statement.

Fundamentals

Nearsightedness is an eye condition where an eye cannot focus on object which are very far. The image of a far object is made in front of retina and not on the retina sue to which it appears to be blurry.

Farsightedness is an eye condition where an eye cannot focus on objects which are very close to the eye. The normal near point of an eye is 25 cm but for a hypermetropic eye, an object placed at this distance will also appear to be blurred. The image is formed behind the retina and not on the retina.

(a)

The lens used to correct nearsightedness is concave lens.

A myopic eye has a certain far point beyond which it cannot focus properly. The image of all the objects beyond the far point will be made in front of retina and not on retina.

The object appears to be at infinity. The lens should be able to focus it on the far point of the person so that it can be seen properly.

If the object is focused at the near point then it will appear to be very close as compared to its actual distance.

If the object is focused closer than the near point then also it cannot be seen properly and it will appear inconveniently very close.

The object is already beyond the far point of the eye. It the lens will focus it at a point farther from the far point, then it will make no sense to use the lens. The object already appears to be blurry.

The lens should form the image at the far point of the eye. The object is at a far distance from the eye so that there is a reasonable distance between the eye and the object.

At the far point, the eye can make a clear image of the object on the retina.

(c)

The lens used to correct nearsightedness is convex lens.

A hypermetropic eye has a certain near point (farther than the near point of a normal eye) before which it cannot focus properly. The image of all the objects near the near point will be made behind the retina and not on retina.

If the object is focused at the near point of the eye so that it can be seen properly.

If the object is focused closer than the near point then also it cannot be seen properly and it will appear inconveniently very close.

The object is placed very near to the eye. If the lens focusses it at a distance farther from the far point. It will appear to be very far away from the eye and will create great confusion

The lens should form the image at the near point of the eye. The object is at a very near distance from the eye so that the image should be formed at the near point of the eye to see it clearly.

At the near point of the eye, the eye can make a clear image of the object on the retina.

Ans: Part a

The lens should form the image at the far point.