A cylindrical mirror

What you can do here
Stand in front of the mirror. Raise one of your hands. What can you see? Observe how the image changes when you move closer or further from the mirror. Conduct the experiment standing on both sides of the mirror.


How it works
Light reflected from a curved surface produces a distorted image of an observed object. The image depends on the curvature of the mirror (magnitude and the side of the mirror where the centre of curvature is) and on the distance of the observed object from the mirror.
The law of reflection states that the angle at which a ray is reflected is the same as the angle at which the incident ray meets the surface (a similar law is used by billiard players). An image is produced at the point where the reflected rays meet – it is a real image, i.e. one that could be screened on a board in front of the mirror (fig. 1). If the reflected rays diverge, an image is produced by extending them “to the other side of the mirror” (fig. 2). That image is virtual, meaning it cannot be seen on a board. If the rays reflected from the mirror are parallel, no image is produced. If you light a mirror with a parallel light beam, all the rays (or their extensions) converge at one point. This point is called focus –real (F) or virtual (F’), and the distance from the focus to the mirror is the focal length. The features of the image depending on the distance from the mirror to the object.
In case of a convex mirror (fig. 2) the image is reduced and your reflection is narrower – and the further from the mirror we stand, the narrower it gets. A concave mirror (fig. 1) makes things look larger when an object is put between the mirror and double focal length (with the exception of the case when the object is at the exact distance of a focal length, where no image is created). Putting an object behind double focal length (point O) gives a reduction effect. Another feature of a concave mirror is that the image of an object put behind the focus is inverted (fig. 1).


Interesting facts
Slimming mirrors are used in some clothes shops. This is done to boost sales by giving an impression that the clothes make the customers look slimmer. The curvature of the mirror surface is very slight so it is barely noticeable.