Background information
A person with normal vision can focus on objects as close as a fewcentimeters from the eye up to objects infinitely far away. Thereexist, however, certain conditions under which the range of visionis not so extended. For example, a nearsighted person cannot focuson objects farther than a certain point (the far point), while afarsighted person cannot focus on objects closer than a certainpoint (the near point). Note that even though the presence of anear point is common to everyone, a farsighted person has a nearpoint that is much farther from the eye than the near point of aperson with normal vision.
Both nearsightedness and farsightedness can be corrected with theuse of glasses or contact lenses. In this case, the eye convergesthe light coming from the image formed by the corrective lensrather than from the object itself.
Part A
When glasses (or contact lenses) are used to correctnearsightedness, where should the corrective lens form an image ofan object located at infinity in order for the eye to form a clearimage of that object?
The lens should form the image at the far point.
Correct
PArt B If a nearsighted person has a far point df thatis 3.50 m from the eye, what is the focal length f1 thecontact lenses that the person would need to see an object atinfinity clearly?
f1 = ? m
Background information
A person with normal vision can focus on objects as close as a fewcentimeters from the eye up to objects infinitely far away. Thereexist, however, certain conditions under which the range of visionis not so extended. For example, a nearsighted person cannot focuson objects farther than a certain point (the far point), while afarsighted person cannot focus on objects closer than a certainpoint (the near point). Note that even though the presence of anear point is common to everyone, a farsighted person has a nearpoint that is much farther from the eye than the near point of aperson with normal vision.
Both nearsightedness and farsightedness can be corrected with theuse of glasses or contact lenses. In this case, the eye convergesthe light coming from the image formed by the corrective lensrather than from the object itself.
Part A
When glasses (or contact lenses) are used to correctnearsightedness, where should the corrective lens form an image ofan object located at infinity in order for the eye to form a clearimage of that object?
The lens should form the image at the far point.
Correct
PArt B If a nearsighted person has a far point df thatis 3.50 m from the eye, what is the focal length f1 thecontact lenses that the person would need to see an object atinfinity clearly?
f1 = ? m
