Spherical MirrorsThe reflecting surface of a spherical mirror may be curved inwards or outwards.A spherical mirror, whose reflecting surface is curved inwards, is called as a concave mirror. A spherical mirror, whose reflecting surface is curved outwards, is called as a convex mirror.
Mirror Versus Shining spoon:The curved surface of the shining spoon will act as a curved mirror. The spherical mirror is the most commonly used mirror. The surface of the spoon curved inwards can be approximated to a concave mirror and the surface of the spoon bulged outwards can be approximated to a convex mirror.
Solar energy concentrated by a concave mirror:Actually solar energy concentrated by a concave mirror at its focus is sufficient to burn the paper. Take a concave mirror of focal length 15 cm or 20 cm. Hold the mirror facing the sun and focus on the paper. Try to obtain the brightest and sharpest spot of concentrated rays on the paper. If you hold your hand steady, you will observe that the piece of paper will begin to burn. This effect is illustrated in the following visual and animation.
Solar energy concentrated by a concave mirror:
In order to discuss the formation of images in spherical mirror, it is necessary to define few terms related to spherical mirrors.
- Centre of Curvature
- Radius of Curvature
- Principal Axis
- Focus and Focal Length
The distance OF, of the focus and the pole of the spherical mirror, is called its focal length, which is denoted by the letter f.
There is a relationship between the radius of curvature R, and focal length f, of a spherical mirror. For spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length.
This implies that the principal focus of a spherical mirror lies midway between the pole and centre of curvature.