Cylindrical mirror

What can you do here
Stand in front of the mirror. Observe how the image changes when you move closer or further from the mirror. Repeat the experiment standing on the other side of the mirror. Take a step aside or wave a hand and notice how strangely your reflection behaves.

How does it work
Light reflected from a curved surface produces distorted image. The image depends on the mirror’s curvature and on the distance of the object being observed from the mirror.

According to the law of reflection, the angle at which the ray is reflected is the same as the angle at which the incident ray meets the surface. The image is produced at the point where the reflected rays meet – it is a real image, so the one that could be screened on a board placed in front of the mirror (fig. 1). If the reflected rays diverge, the image is created by extending them “to the other side of the mirror” (fig. 2). That image is virtual.

If we light the mirror with a parallel light beam, all the rays (or their extensions) converge at one point. This point is called a focus – a real one (F) or a virtual one (F’), and the distance from the focus to the mirror is the focal length. In case of a convex mirror (fig. 2) the image is reduced and our reflection is narrower – and the further from the mirror we stand, the narrower it gets. A concave mirror (fig. 1) makes things look wider when we stand between the mirror and double focal length (with the exception of the case when we stand at the exact distance of a focal length, where no image is created). Standing behind the focus results in slimming effect. Another feature of a concave mirror is that the image of an object placed behind the focus is inverted.

Interesting facts
Convex mirrors of small curvature are used in clothing shops in order to achieve the effect of slim figure.