Question

An object is placed at a distance of 10 cm in front of a concave mirror of focal length 15 cm. Use mirror formula to determine the position of the image formed by this mirror.

Answer 1

Given:

Object distance (u) = −10 cm

Focal length (f) = −15 cm

Image distance (v) = ?

Using the mirror formula, we get 

`1/f = 1/v + 1/u` 

`1/(-15) = 1/v + 1/(-10)` 

`1/v = 1/(-15) - 1/(-10)` 

`1/v = 1/(-15) + 1/10`   ...[Taking LCM of 15 and 10, is Which 30]

`1/v = (-2)/30 + 3/30` 

`1/v = (-2 + 3)/30` 

`1/v = 1/30` 

∴ v = 30 cm

The image is formed at a distance of 30 cm behind the mirror. The positive value of v indicates that the image is formed on the same side as the object, meaning it is a virtual and erect image.