For a myopic person with a far point of 80 cm, a concave lens is needed for correction. The focal length of the lens, f, is equal to the far point distance, which is -80 cm (negative because it’s a concave lens). The power P of the lens is calculated using P = 1/f, where f is in meters. Thus, P = 1/−0.80 = −1.25 dioptres. The required lens is concave with a power of -1.25 dioptres.
Let’s discuss in detail
Correcting Myopia: Lens Requirements for a Specific Case
Understanding Myopia and Far Point: Myopia, or near-sightedness, is a condition where distant objects appear blurry. The far point in myopia is the farthest distance at which objects are seen clearly. For the person in question, this distance is 80 cm, indicating that they cannot see objects clearly beyond this point.
The Role of Concave Lenses in Myopia
To correct myopia, concave lenses are used. These lenses diverge light rays, effectively extending the point where the image comes into focus onto the retina. This adjustment allows for clear vision of distant objects.
Determining the Focal Length
The focal length of the corrective lens is crucial. In this case, the far point of the person is 80 cm from the eye. Therefore, the focal length of the required lens is -80 cm (negative sign indicates a concave lens).
Calculating the Power of the Lens
The power of a lens (P) is calculated using the formula P =1/f, where f is the focal length in meters. For a focal length of -80 cm, or -0.80 meters, the power is P = 1/−0.80.
Resulting Lens Power
The calculation yields a lens power of -1.25 dioptres. This value indicates the strength of the concave lens needed to correct the myopic condition of the individual.
Conclusion: Lens Specification
To correct the myopic condition of this individual, a concave lens with a power of -1.25 dioptres is required. This lens will enable them to see distant objects clearly, correcting the short-sightedness caused by their myopia.