For a person suffering from myopia (short sightedness), which type of corrective lens is used to improve distant vision?

Introduction / Context:
Defects of vision and their correction are classic topics in physics and biology, especially in school level examinations. Myopia, also known as short sightedness, is a condition in which a person can see nearby objects clearly but has difficulty seeing distant objects. This question tests whether you know which optical lens is used in spectacles to correct myopia and restore clear vision for far objects.

Given Data / Assumptions:

• The person is suffering from myopia or short sightedness.
• The question asks specifically about the type of lens used for correction.
• Four options are provided: convex, concave, crossed, and cylindrical lenses.
• We assume standard school level definitions of these lenses and eye defects.

Concept / Approach:
In a myopic eye, the eyeball is effectively too long or the eye lens has too much converging power. As a result, light rays coming from distant objects converge to form an image in front of the retina instead of exactly on it. To correct this, we must decrease the overall converging power of the eye. This can be achieved by placing a diverging lens in front of the eye, which spreads out the incoming parallel rays before they enter the eye, so that the eye lens forms the image on the retina. A diverging lens is a concave lens. Convex lenses are converging lenses and are used for hypermetropia, not myopia.

Step-by-Step Solution:

Verification / Alternative check:
An alternative check is to remember the standard matching of eye defects and lenses: myopia is associated with concave lenses, hypermetropia with convex lenses, and astigmatism with cylindrical lenses. Crossed lenses are not a standard category in basic optics. This standard association provides a quick verification that concave lens is the correct choice for myopia.

Why Other Options Are Wrong:

• Convex lens: This is a converging lens and would increase the total power of the eye, which would worsen myopia instead of correcting it.
• Crossed lens: This is not a standard optical lens type used for correcting simple refractive errors in basic physics or biology curricula.
• Cylindrical lens: Used to correct astigmatism, where the curvature of the cornea is irregular, not for simple myopia alone.

Common Pitfalls:
Students sometimes confuse the lenses used for myopia and hypermetropia, especially under exam pressure. Another pitfall is to assume that any lens that looks thick at the centre must be correct, without recalling whether a converging or diverging effect is needed. It is also important not to mix up cylindrical lenses, which are prescribed specifically for astigmatism, with lenses used for simple short sightedness.

Final Answer:
The corrective lens used for a person suffering from myopia is a Concave lens.