- Spherical mirrors are a part of a sphere
- Generally, the smaller piece is used as a mirror.
- If a mirror is obtained from a sphere silvered on the outer side, it is called a concave mirror
- If a mirror is obtained from a sphere silvered inside, it is called a convex mirror
Terms relating to spherical mirrors
- Length MM’ is the measure of aperture, C is the centre of curvature, P is the pole, and PC is the principal axis.
The portion available for reflection is called aperture; MPM’ is the aperture.
It is the geometric centre of the reflecting surface. P is the pole.
- Centre of curvature
It is the centre of the sphere of which the mirror forms a part. C is the centre of curvature.
- Principal axis
It is the straight line passing through the centre of curvature and the pole.The line passing through P and C in the figure is the principal axis.
- Radius of curvature (R)
It is the radius of the sphere of which the mirror forms a part. PC is the radius of curvature.
- Principal focus
In case of the concave mirror, the parallel beam after reflection converges at a point F called the principal focus.
In case of a convex mirror,it appears to diverge from a point F called the focus
- Focal length
It is the distance between the pole and the principal focus.PF is the focal length. Focal length is measured in m or cm.
for a spherical mirror, the radius of curvature is twice its focal length.
- The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror, the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be :
(a) 1 m/s (b) 2 m/s (c) 4 m/s (d) 8 m/s
Formation of image by concave mirror
- AB is an extended object and A1B1 is an image formed by the concave mirror of small aperture
- When a lighted bulb is placed at the focus of a concave mirror reflector, the diverging light rays of the bulb are collected by the concave reflector and then reflected to produce a strong, parallel-sided beam of light
Uses of Concave Mirrors
- Concave mirrors are used as shaving mirrors to see a large image of the face.
- Concave mirrors are used by dentists to see the large images of the teeth of patients.
- Concave mirrors are used as reflectors in torches, vehicle head-lights and search lights to get powerful beams of light
- Large concave mirrors are used in the field of solar energy to focus sun’s rays for heating solar furnaces.
Formation of image by convex mirror
Uses Of Convex Mirror
- Image formation by a Convex Mirror used as rear-view (wing) mirrors in vehicles.
- These mirrors are fitted on the sides of the vehicle, enabling the driver to see traffic behind him/her to facilitate safe driving.
- Convex mirrors are preferred because they always give an erect, though diminished, image.
- Also, they have a wider field of view as they are curved outwards. Thus, convex mirrors enable the driver to view much larger area than would be possible with a plane mirror.