Mirror Imaging Visualization
Mirror Parameters
Object Position
Ray Tracing Options
Mirror Properties
Mirror Imaging Formulas
Instructions
- Adjust object distance and height to see how the image changes
- Toggle ray tracing to visualize light paths and virtual image formation
- Move the eye position to explore the field of view
- Observe how rays appear to diverge from the virtual image behind the mirror
- Notice the symmetry: object and image are equidistant from the mirror
What is Plane Mirror Imaging?
Plane mirror imaging is based on the law of reflection: when light rays strike a mirror, they reflect such that the angle of incidence equals the angle of reflection. The image formed in a plane mirror is always virtual (cannot be projected on a screen), upright, and the same size as the object. The image appears to be located behind the mirror at the same distance as the object is in front of it.
Virtual Image Formation
A virtual image is formed when light rays appear to diverge from a point behind the mirror. Unlike real images, virtual images cannot be projected onto a screen because no light actually passes through the image location. In a plane mirror, the reflected rays appear to come from a point behind the mirror at the same distance as the object is in front. Our brain traces these rays backward and perceives an image at that location.
Symmetry Principle
Plane mirrors create perfectly symmetrical images. Every point on the object has a corresponding point on the image that is equidistant from the mirror but on the opposite side. This symmetry means: (1) The image distance (d_i) equals the object distance (d_o) in magnitude, (2) The image height (h_i) equals the object height (h_o), (3) Left and right are reversed (lateral inversion), and (4) The image is always upright. This symmetry is why text appears reversed when viewed in a mirror.
Ray Tracing Rules
To locate the image formed by a plane mirror, we can trace any two rays from an object point: (1) A ray perpendicular to the mirror reflects back along the same path, and (2) A ray at an arbitrary angle reflects such that the angle of incidence equals the angle of reflection. When these reflected rays are extended backward (shown as dashed lines), they intersect at the image location. This intersection point is where the virtual image appears to be. The law of reflection (θ_i = θ_r) is fundamental to all mirror systems.
Field of View
The field of view in a plane mirror is the area within which the observer can see the image. It depends on: (1) The size of the mirror, (2) The distance of the observer from the mirror, and (3) The position of the object. To see the full image of an object in a plane mirror, the mirror needs to be at least half the height of the object. This is why a dressing mirror needs to be at least half your height to see your full reflection. The field of view can be visualized by drawing rays from the image to the observer's eye.
Practical Applications
Plane mirrors are everywhere in daily life and technology. Dressing mirrors and bathroom mirrors allow us to see ourselves for grooming. Periscopes in submarines use two plane mirrors to see above the water surface. Kaleidoscopes use multiple plane mirrors to create symmetrical patterns. Optical instruments often contain plane mirrors to redirect light paths. Rearview mirrors in cars help drivers see behind. Solar mirrors in power plants concentrate sunlight using arrays of flat or slightly curved mirrors. Understanding plane mirror imaging is fundamental to geometric optics and the design of more complex optical systems.
Lateral Inversion
One interesting property of plane mirrors is lateral inversion: left and right are swapped. When you raise your left hand, your mirror image appears to raise its right hand. This happens because the mirror reverses the coordinate system perpendicular to its surface. However, up and down are NOT inverted - the top of the object remains at the top in the image. This selective inversion is a direct consequence of the symmetric imaging property. Understanding lateral inversion explains why text appears reversed in mirrors and why ambulance signs are sometimes printed backward to read correctly in rearview mirrors.