Light Reflection and Refraction NCERT Solution, study material, CBSE Notes

NCERT Solution: Light Reflection and Refraction

Draw ray diagrams showing the image formation by a concave lens when an object is placed
(c) beyond twice the focal length of the lens

Draw ray diagrams showing the image formation by a convex mirror when an object is placed
(a) at infinity

Draw ray diagrams showing the image formation by a convex mirror when an object is placed(b) at finite distance from the mirror

The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is 80 cm, at what distance should the candle be placed from the lens? What is the nature of the image at a distance of 80 cm and the lens?

Magnification is 3 times and image distance v=80 cm

Since, object distance is taken as negative; as per sign convention so,

or, u = - 80 / 3 cm

Nature of image: Since image is formed on the other side of lens hence it is a real image and inverted image.

Nature of Lens: Enlarged image is formed by convex lens and not by concave lens, so it is a convex lens.

Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?

. The degree of divergence or convergence achieved by a given lens is called power of the lens. The unit of power of lens is diopter and is expressed by D. Focal length of lens used by first student is in positive hence it is a convex lens. The lens of second student is a concave lens.

Power of lens (first student) =+2

Power of lens (second student) =-2

Size of image of an object by a mirror having a focal length of 20cm is observed to be reduced to 1/3rd of its size. At what distance the object has been placed from the mirror? What is the nature of the image and the mirror?