(i) Define power of a lens. Write its SI unit. (ii) You are provided with two convex lenses of focal length 15 cm and 25 cm, respectively. Which of the two is of larger power? Give reason for you answer. (iii) A 20 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10cm. The distance of the object the lens is 15 cm. Find the nature, position and size of the image. Alsofind its magnification.

(i) Define power of a lens. Write its SI unit. (ii) You are provided

1.	(i) Define power of a lens. Write its SI unit. (ii) You are provided with two convex lenses of focal length 15 cm and 25 cm, respectively. Which of the two is of larger power? Give reason for you answer. (iii) A 20 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10cm. The distance of the object the lens is 15 cm. Find the nature, position and size of the image. Alsofind its magnification.
Answer» Solution :(i) Ability of a lens to converge or diverge light rays is TERMED as power of a lens. Power `=1/("Focal length")` SI UNIT of power is Diptre. (ii) Lens of focal length 15 cm is of larger power because power is inversely proportional to the focal length. (iii) `1/v-1/u=1/f` `1/v=1/(-15)+1/10` `=1/30:.v=30` cm IMAGE is real and inverted Magnification `=(h.)/h=v/u,m=-2`