Define the following terms :(i) Power of a lens (ii) Principal focus of a concave mirror(b) Write the relationship among the object distance (u), image distance (v) and the focal length (f) of a(i) Spherical lens(ii) Spherical mirror(c) An object is placed at a distance of 10 cm from optical centre of a convex lens of focal length 15 cm. Draw a labelled ray diagram to show the formation of image in this case.

Define the following terms :(i) Power of a lens (ii) Principal focus o

1.	Define the following terms :(i) Power of a lens (ii) Principal focus of a concave mirror(b) Write the relationship among the object distance (u), image distance (v) and the focal length (f) of a(i) Spherical lens(ii) Spherical mirror(c) An object is placed at a distance of 10 cm from optical centre of a convex lens of focal length 15 cm. Draw a labelled ray diagram to show the formation of image in this case.
Answer» SOLUTION : (i) Power of a lens is a measure of the degree of convergence or divergence of light rays achieved by it. Mathematically, power (P) of a lens is defined asreciprocal of its focal length i.e., P=`1/f` (ii) Principal focus of a concave mirror is a point situated on its principal axis, where light rays COMING parallel to the principal axis of mirror, after reflection, actuallynconverge. (b) (i) `1/v-1/u=1/f` (ii) `1/v+1/u=1/f` (c) A labelled ray diagram is drawn below : A virtual, ERECT and ENLARGED image is being formed on same SIDE of lens at a distance of 30 cm from optical centre of lens.