As you know, a plane mirror is simply a flat mirror in which an object is reflected. In order to explain how the human eye forms an image of the light source behind the opaque mirror, we can use light rays and the laws of reflection:
The incident rays from the light source reflect off the plane mirror and hit our eye. because our brain projects the reflected rays behind the mirror, meaning the light rays do not actually reach the image, we call it a virtual image. It is the same distance behind the mirror as the real object is in front. In order to find the equal distance between the two, we use what’s called an object-image line (in red):
This is a parallel line. We can use object-image lines to determine where a virtual image will be.
We use four characteristics to describe the behaviour of an image. They form the acronym SALT:
- S: size. Is the image larger, smaller, or the same size as the object?
- A: attitude. Is the image upright or inverted (upside-down)?
- L: location. Where is the image located?
- T: type. Is the image real or virtual?
When using a plane mirror, the image is always the same size, upright but laterally inverted, behind the mirror, and virtual.