Question

an object is placed at a distance of 45 cm in front of a convex lens of focal length 30 cm between f and 2f then position of the image will be​

Answer 1

Answer :-

Position of the image is at 90 cm on the other side of the lens . (Beyond 2f') .

Explanation :-

We have :-

→ Distance of object (u) = 45 cm

→ Focal length of mirror (f) = 30 cm

________________________________

According to sign convention, we know that the object distance is always negative i.e. -45 cm and focal length of a convex mirror is always positive i.e. + 30 cm.

Now, putting values in the lens formula :-

1/v - 1/u = 1/f

⇒ 1/v = 1/f + 1/u

⇒ 1/v = 1/30 + 1/(-45)

⇒ 1/v = 1/30 - 1/45

⇒ 1/v = (3 - 2)/90

⇒ 1/v = 1/90

⇒ v = 90 cm

Answer 2

Given,

•Distance of object (u) = -45 cm

•Focal length of LENS (f) = +30 cm

Need to find :

• Position of image = ?

Solution :

Substituting the values in the lens formula we get,

1/v - 1/u = 1/f

⇒ 1/v = 1/30 - 1/45

⇒ 1/v = (3 - 2)/90

⇒ 1/v = 1/90

⇒ v = 90 cm