A certain child’s near point is 10.0 cm; her far point (with...

Name: Problem 12, Chapter 25: College Physics
Uploaded: 2020-03-29T18:46:50-08:00
Duration: 5 min 26 s
Channel: Netra Sharma
Description: A certain child’s near point is 10.0 cm; her far point (with eyes relaxed) is 125 cm. Each eye lens is 2.00 cm from the retina. (a) Between what limits, measured in diopters, does the power of this lens–cornea combination vary? (b) Calculate the power of the eyeglass lens the child should use for relaxed distance vision. Is the lens converging or diverging?

A certain child’s near point is 10.0 cm; her far point (with eyes relaxed) is 125 cm. Each eye lens is 2.00 cm from the retina. (a) Between what limits, measured in diopters, does the power of this lens–cornea combination vary? (b) Calculate the power of the eyeglass lens the child should use for relaxed distance vision. Is the lens converging or diverging?

Key Concepts

Diopter

A diopter is the unit used to measure the optical power of a lens. It is defined as the reciprocal of the focal length in meters (1/m). This measurement is central in optometry because it quantifies how strongly a lens converges or diverges light, enabling the correction of refractive errors.

Accommodation

Accommodation refers to the eye’s ability to adjust its optical power to focus on objects at various distances. It involves changing the shape of the eye’s lens so that the image of an object, whether near or far, is sharply focused on the retina. The range of accommodation is often expressed in diopters as the difference between the powers required for the near point and the far point.

Near Point and Far Point

The near point is the closest distance at which the eye can form a clear image, while the far point is the most distant point at which the eye can focus without strain when relaxed. These distances are critical in diagnosing refractive errors and determining the necessary corrective power, as the eye’s natural limits dictate the range over which it must adjust to maintain clear vision.

Corrective Lenses

Corrective lenses are used to assist the eye in focusing images onto the retina, compensating for limitations in the eye’s natural accommodation. By adding a lens with the appropriate power, the effective focal length of the eye’s optical system is altered so that objects at a desired distance (often infinity for relaxed viewing) are brought into clear focus. The type of lens (converging or diverging) is determined by whether the eye is underpowered or overpowered relative to the optimal focusing needs.

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