Question

an object 4 cm high is placed 15 cm from a convex lens of focal length 5 cm. draw a ray diagram on graph paper and find position , nature and size of the image

Answer 1

Explanation:

object's height, h_0h

0

= 4cm

object distance , u = -15cm

focal length of convex lens , f = +5cm

using lens maker formula,

1/v - 1/u = 1/f

or, 1/v - 1/-15 = 1/5

or, 1/v = 1/5 - 1/15 = 2/15

or, v = 15/2 = +7.5 cm

as image distance is positive, image is real and it is located at 7.5cm behind the lens ( right side).

magnification, m = v/u = height of image /height of object.

or, (+7.5)/(-15cm) = height of image/(4cm)

or, height of image = -2cm < height of object

hence, image is real and diminished.

see diagram , which shows image position, nature and size.