An object of height 4 cm is placedin front of a concave lens of focal length 40 cm. If the objectdistance is 60 cm, find the position and height of the image.

An object of height 4 cm is placedin front of a concave lens of focal

1.	An object of height 4 cm is placedin front of a concave lens of focal length 40 cm. If the objectdistance is 60 cm, find the position and height of the image.
Answer» Solution :` (i) 1/f = 1/v -1/u"" therefore 1/u = 1/f + 1/u` ` therefore 1/u = 1/( - 40 cm) + 1/( - 60 cm) = - (1/( 40 cm) + 1/( 60 cm) )` ` = - ((3+2)/(120 cm) ) = - 5/120 cm` ` v - (120 cm)/5 = - 24 cm ` The image is FORMED at 24 cm from the lens. It is on the same side as the object. (II) ` h_(2)/h_(1) =u/v"" therefore h_(2) = v/u h_(1)` ` thereforeh_(2) = ((-24 cm)/(- 60 cm)) xx 4 cm = 0.4 xx 4 cm = 1.6 cm` The height of the image is 1.6 cm