Question

The power of lens in the spectacles of a person is +2D. The person suffers from:
A. Hypermetropia
B. Myopia
C. Colour blindness
D. Presbyopia

Answer 1

Hint: In this question we have been asked to determine the eye defect the person is suffering from. It is given that the power of the lens used by the person is +2D. Therefore, to solve this question, we shall first calculate the focal length of the lens. We shall then determine the lens that has the same focal length. Now, we know that specific lenses are used to correct respective eye defects. Therefore, using this concept we shall determine what the person is suffering from.

Formula used:
\[P=\dfrac{1}{f}\]
Where,
P is the power and f is the focal length

Complete step-by-step answer:
It is given that the person uses the lens of power +2D. Now, we know that the power of a lens if given as the reciprocal of focal length
Therefore,
\[P=\dfrac{1}{f}\]
After substituting power along with the signs and conventions we get,
\[f=+\dfrac{1}{2}\]
Now, we know that the positive focal length is always positive for a converging lens. It means that focal length is positive for a convex lens, since it is a converging lens.
We also know that the convex lens is used to converge the rays falling behind the retina. These rays are converged at the retina using the convex lens. The eye defect in which the rays converge behind the retina is known as hypermetropia. Therefore, a convex lens is used to cure hypermetropia.

So, the correct answer is “Option A”.

Note: When the rays from the nearby objects converge behind the retina and the object looks blur, such eye defect is known as Hypermetropia. In hypermetropia, the person can see distant objects clearly but the nearby object looks blurred. Hypermetropia is corrected by using a suitable convex lens. The convex lens converges the image on the retina making nearby objects clearly visible.