uv (cm 2) Slope=f (u+v) cm. If we repeat this process for point $$P′P′$$, we obtain its image at point $$Q′$$. The number of images formed by two adjacent plane mirrors depends on the angle between the mirror. You may have noticed that image 3 is smaller than the object, whereas images 1 and 2 are the same size as the object. And with the sign conventions we just discussed and the signs I'm using in this formula, concave mirrors always have a positive focal length. The image formed by a plane mirror is always virtual (meaning that the light rays do not actually come from the image), upright, and of the same shape and size as the object it is reflecting. To find image 1,2, you have to look behind the corner of the two mirrors. A plane mirror is made using some highly reflecting and polished surface such as a silver or aluminium surface in a process called silvering. It may be written as, where, v = Distance of image from pole of mirror u = Distance of object from pole of mirror Concave and Convex mirrors (spherical mirrors)[5] are also able to produce virtual images similar to a plane mirror. which is called the “ small-angle approximation ”), then FX ≈ FP or CF ≈ FP. If θ (in degrees) is angle between the plane mirrors then number of images are given by, n = 360 θ − 1. The reflecting surface reflects most of the light striking it as long as the surface remains uncontaminated by tarnishing or oxidation. Applying this to triangles PAB and QAB in and using basic geometry shows that they are congruent triangles. b. The law of reflection tells us that the angle of incidence is the same as the angle of reflection. The mirror equation $$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$$ holds good for concave mirrors as well as convex mirrors. Images in a plane mirror are the same size as the object, are located behind the mirror, and are oriented in the same direction as the object (i.e., “upright”). and, f = Focal length of the mirror. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. In a convex mirror, the virtual image formed is always diminished, whereas in a concave mirror when the object is placed between the focus and the pole, an enlarged virtual image is formed. The difference is that a virtual image cannot be projected onto a screen, whereas a real image can. Given picture below shows how we can find the image of a point in plane mirrors. The object distance (denoted $$d_o$$) is the distance from the mirror to the object (or, more generally, from the center of the optical element that creates its image). The number of images depends on the angle between the two mirrors. You should convince yourself by using basic geometry that the image height (the distance from $$Q$$ to $$Q′$$) is the same as the object height (the distance from $$P$$ to $$P′$$). This work is licensed by OpenStax University Physics under a Creative Commons Attribution License (by 4.0). Describe how an image is formed by a plane mirror. If you walk behind the mirror, you cannot see the image, because the rays do not go there. For more information contact us at [email protected] or check out our status page at https://status.libretexts.org. Therefore, in applications where a virtual image of the same size is required, a plane mirror is preferred over spherical mirrors. Inserting this into Equation 2.3.1 for the radius R, we get. [citation needed] The focal length of a plane mirror is infinity;[4] its optical power is zero.