Question

A concave lens is used:

• A. as magnifying lens
• B. in a car to see objects on rear
• C. in spectacles for the correction of short sightedness
• D. in simple cameras

Hint:

Concave lenses are used in spectacles for myopia correction, as they diverge light to bring distant objects into focus.

Answer 1

The Correct Option is C

A concave lens is a type of diverging lens that is thinner at the center than at the edges. It is commonly used in the correction of short-sightedness, or myopia, and has several important optical properties that make it suitable for this purpose. \smallskip 1.
Correcting Short-Sightedness (Myopia):

Short-sightedness, or myopia, occurs when the image of a distant object is focused in front of the retina, making it appear blurry. This happens because the eye's lens focuses light rays too strongly.
A concave lens diverges the incoming light rays before they enter the eye. This diverging effect causes the rays to spread out, and as a result, the image is focused further back onto the retina, allowing the person to see distant objects clearly.
\smallskip 2.
Diverging Light Rays:

The concave lens works by spreading the light rays apart. This divergence of light reduces the focal length of the lens, thus correcting the over-convergence of light that causes blurred vision in myopic individuals.
The diverging rays from a concave lens appear to originate from a virtual focus on the same side of the lens as the object, which aids in focusing the image directly onto the retina.
\smallskip 3.
Why Concave Lenses are Not Used as Magnifying Lenses:

Concave lenses are not used for magnification because they produce virtual, diminished, and upright images. A magnifying lens typically needs to produce a larger, upright, and virtual image, which is achieved using convex lenses (which converge light).
Since concave lenses cause light rays to diverge, they would not provide the magnification effect needed to enlarge objects.
\smallskip 4.
Concave Lenses in Rear-View Mirrors and Cameras:

Concave lenses are not used in rear-view mirrors in cars because they would cause the image to appear smaller and inverted. Convex mirrors are preferred for rear-view mirrors because they provide a wider field of view and produce smaller, upright images.
In simple cameras, concave lenses are not commonly used because they do not produce sharp images. Cameras require lenses that converge light to focus it accurately onto a film or digital sensor, which is typically achieved using convex lenses.
\smallskip In summary, concave lenses are primarily used to correct myopia by diverging light rays before they reach the eye, helping individuals with short-sightedness see distant objects clearly. However, they are not suitable for magnification, rear-view mirrors, or simple cameras due to their divergent nature and the types of images they produce.