(a) Draw a ray diagram to show the formation of image of an object placed between infinity and optical centre of a concave lens. (b) A concave lens of focal length 15 cm forms an image 10 cm from the lens. Calculate (i) the object distance, (ii) the nature and magnification of the image formed.

(a) Draw a ray diagram to show the formation of image of an object pla

1.	(a) Draw a ray diagram to show the formation of image of an object placed between infinity and optical centre of a concave lens. (b) A concave lens of focal length 15 cm forms an image 10 cm from the lens. Calculate (i) the object distance, (ii) the nature and magnification of the image formed.
Answer» Solution :(a) A ray diagram showing the FORMATION of image of an object placed between infinity and optical CENTRE of a concave lens is shown below. (b) Here f = - 15 cm, v = - 10 cm (i) From lens FORMULA `(1)/(v) - (1)/(u) = (1)/(f)`, we have `(1)/(u) = (1)/(v) - (1)/(f) = (1)/((-10)) - (1)/((-15)) = - (1)/(10) + (1)/(15) = - (1)/(30)` `rArr""u = - 30` cm THUS, the object is placed at a distance of 30 cm from the concave lens and the image is a virtual image. (ii) Magnification `m = (v)/(u) = ((-10))/((-30)) = (1)/(3) = 0.33`