Plane Mirror: Object Distance Equals Image Distance

A plane mirror is a mirror with a flat reflective surface. When an object is placed in front of a plane mirror, it forms a virtual, erect, and laterally inverted image behind the mirror. A key characteristic of the image formed by a plane mirror is its position relative to the mirror.

Understanding the Distances

The distance of the object from the mirror is called the object distance, often denoted by '$u$'. The distance of the image from the mirror is called the image distance, often denoted by '$v$'.

For a plane mirror, the following properties hold true for the image formed:

• The image is virtual (cannot be projected on a screen).
• The image is erect (upright).
• The image is the same size as the object.
• The image is laterally inverted (left and right are reversed).
• The image is formed as far behind the mirror as the object is in front of it.

Distance Relationship Explained

Based on the property that the image is formed as far behind the mirror as the object is in front, the magnitude of the object distance is equal to the magnitude of the image distance.

Mathematically, if we consider the distances as positive magnitudes:

Object distance = Image distance

Or using standard notation, where distances are measured from the pole of the mirror:

$$ |u| = |v| $$

Therefore, the object distance and the image distance are always equal for a plane mirror.