Question

The focal length of a convex lens is 5cm, where should the object be placed to get a real image with same size as that of object.

Answer 1

Answer:

For convex lens sign convention is-

V=+ve

a=−ve

f=+ve

I (length of image) =−ve (real image)

O (size of object) =+ve

So, using lens formula

−

+O

−I

=

u

+V

⇒u=−

3

v

⇒v=−3u

v

1

−

u

1

=

f

1

⇒

−3u

1

−

u

1

=

f

1

⇒

3u

4

=−

15

1

⇒u=−20cm

object is placed 20cm in front of the lens

Explanation:

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