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Image Formed By Spherical Mirrors and Uses of Concave and Convex Mirror

Spherical mirror

  • 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.
  1. Aperture
    The portion available for reflection is called aperture; MPM’ is the aperture.
  2. Pole
    It is the geometric centre of the reflecting surface. P is the pole.
  3. Centre of curvature
    It is the centre of the sphere of which the mirror forms a part. C is the centre of curvature.
  4. 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.
  5. Radius of curvature (R)
    It is the radius of the sphere of which the mirror forms a part. PC is the radius of curvature.
  6. 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
  7. 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.

Question –

  1. 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.
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