Question

An object is placed at a distance of 30 cm in front of a convex lens of focal length 15 cm. Use lens formula to determine the position of the image. What will be the size of the image in this case?

Answer 1

Given: Object distance (u) = −30 cm (in front of lens)

Focal length (f) = +15 cm (convex lens)

By using the lens formula:

`1/f = 1/v - 1/u`

⇒ `1/15 = 1/v - (-1/30)`

⇒ `1/15 = 1/v + 1/30`

⇒ `1/v = 1/15 - 1/30`

⇒ `1/v = (2 - 1)/30`

`1/v = 1/30`

v = +30 cm

The image is formed 30 cm on the other side of the lens.

Magnification (m) = `v/u`

= `30/-30`

= −1

The image is real, inverted, and equal in size to the object.