Question

Q.28. In adjoining figure an optical device is
placed inside the box drawn. Light beam entering
into the box and emerging out of box have also
been shown. The box is
(a) a concave lens.
(6) a glass slab.
(c) a glass prism.
d) a convex lens.
[CBSE 2011, 2014]
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Answer 1

Answer:

A-concave lens as in the given pic the rays of light diverges

Answer 2

Based on the path of the light beam shown in the figure, the optical device placed inside the box must be a concave lens.(Option A)

• A concave lens is a type of optical lens that is thinner in the center than at the edges. It is also known as a diverging lens, as it causes a beam of light to spread out or diverge.
• Concave lenses are used to correct nearsightedness or myopia. This is because they diverge the light rays before they enter the eye, which allows the image to be focused correctly on the retina.
• Concave lenses are used in a variety of optical devices, such as microscopes, telescopes, and cameras, to help magnify objects and produce clearer images.
• The focal length of a concave lens is a negative value, as the lens causes light rays to diverge rather than converge. The focal length is the distance from the lens at which parallel light rays converge.
• Objects viewed through a concave lens will appear smaller and farther away than they actually are. This is because the lens spreads out the light rays, making the image appear smaller.
• Concave lenses are used in combination with convex lenses to correct vision problems such as presbyopia or astigmatism. This combination of lenses is often used in eyeglasses or contact lenses to help people see more clearly.
• The power of a concave lens is measured in diopters (D), which is equal to the reciprocal of the focal length in meters. A lens with a focal length of -1 meter has a power of -1 D.

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