Question

Find the position, size and nature of the image formed when an object 2 cm high is placed.
A) 7.5 cm from a convex lens of a focal length of 5cm.
B) 4 cm from a convex lens of focal length 12 cm.
C) 10 centimetre from a concave lens of focal length 10cm

Answer 1

Explanation:

given height of the object = 2cm

A) given, u = -7.5cm

f = 5cm

lens formula :- 1/v - 1/u = 1/f

1/v +10/75 = 1/5

1/v = 1/5 - 2/15

v = 15 cm

magnification = v/u

= 15/ -7.5

magnification = 2cm

therefore the image is placed 15cm far from the lens and image is enlarged by 2cm

B) given, u = -4cm

f = 12cm

lens formula :- 1/v -1/u = 1/f

1/v +1/4= 1/12

1/v = 1/12 -1/ 4

v = -6cm

magnification = v/u

= 6/4

magnification= 1.5cm

therefore the image is placed 6cm far from the lens, and the image real image, and is enlarged by 1.5cm