Far point defective eye = focal length of the concave mirror.
.•. 2cm = -2cm

we know that. power =100/f(in m)


p=100/-2

.•. p= -50 D

Calculating the Power of the Lens to Correct Short Sightedness

To calculate the power of the lens required to correct the vision of a short-sighted person, we need to understand how the eye works and how lenses can be used to correct refractive errors.

Understanding Short Sightedness (Myopia)
Short-sightedness, or myopia, is a common refractive error where the eyeball is slightly longer than usual or the cornea is too curved. This causes light to focus in front of the retina, resulting in a blurry image for objects that are far away.

Converting Distance to Diopters
To calculate the power of the lens, we need to convert the distance at which the person can see clearly into diopters. Diopters are the unit of measurement for the refractive power of a lens. The formula to convert distance (in meters) to diopters is:

Power (D) = 1 / distance (m)

In this case, the person can see clearly up to a distance of 2cm, which is 0.02 meters. So the power of the lens required to correct their vision would be:

Power (D) = 1 / 0.02 = 50 D

Selecting the Correct Lens
Now that we know the power of the lens required to correct the short-sightedness, we need to select the correct lens. Lenses have a positive or negative power, depending on whether they correct myopia (negative power) or hyperopia (positive power).

In this case, since the person is short-sighted, we need to select a lens with a negative power. The lens should have a power of -50 D to correct the vision and bring the focal point back onto the retina.

Consulting an Optometrist
It is important to note that calculating the power of the lens is a simplified approach and should not replace a proper eye examination by an optometrist. Optometrists use various techniques and tests to determine the exact prescription needed for each individual.

Conclusion
To correct the vision of a short-sighted person who cannot see clearly beyond 2cm, a lens with a power of -50 D would be required. It is essential to consult an optometrist for a comprehensive eye examination and to obtain the correct prescription tailored to the individual's specific needs.