Question

The magnification of an object formed by a lens is of magnification -1. If the distance between the object and the image is 60 cm, what is the focal length of the lens? If the object is moved 20 cm towards the lens , where would be the image formed? State the reason

Answer 1

Answer:

Explanation:

Magnification (m) = -1

∴ m = v/u

-1 = v/u

v = -u

v + u = 0 ------------ eq (1)

According to the Question,

∴ v - u = 60 --------------eq (2)

Solving the equations simultaneously,

v = 30 cm

∴ u = v - 60

= 30 - 60

= -30 cm.

Now, Using the lens Formula,

⇒

⇒f = 15 cm.

Thus, the focal length of the lens is 15 cm.

Now, In second case,

Object is shifted 20 cm towards the lens,

Thus, u = -30 + 20

u = -10 cm

Now, Again using the lens Formula,

v = - 30 cm.

Thus, the image is formed 30 cm behind the object i.e., on the same side of the lens.