Mirrors

Why is an Image Formed?

In order to view an object, you must sight along a line at that object; and when you do light will come from that object to your eye along the line of sight.

This very principle can be extended to the task of viewing the image of an object in a plane (i.e., flat) mirror:

In order to see the image of an object in a mirror, you must sight at the image; when you sight at the image, light will come to your eye along that line of sight.

This principle can be illustrated in one of our Physics class using a plane mirror and an object. The object is placed in front of the mirror and students from different locations in the room are asked to sight at its image. Regardless of who is viewing the image and from where they are viewing the image, each sight line must intersect in the same location. 

Plane Mirrors

In the case of plane mirrors, the image is said to be a virtual image. Virtual images are images that are formed in locations where light does not actually reach. Light does not actually pass through the location on the other side of the mirror; it only appears to an observer as though the light is coming from this location. Whenever a mirror (whether a plane mirror or otherwise) creates an image that is virtual, it will be located behind the mirror where light does not really come from. Such images are formed on the same side of the mirror as the object and light passes through the actual image location.

Besides the fact that plane mirror images are virtual, there are several other characteristics that are worth noting.

• Laterally Inverted images
• Upright
• Same Distance between the image and the object