Plane Mirror

  • The image formed by a plane mirror is erect, laterally inverted and virtual. Also, it has the same size as the object and is as far behind the mirror as the object is in front of it.
  • A polished surface is visible only from that direction in which it reflects the light.
  • In reflection from irregular surfaces, the object can be seen from all directions.
  • A man can see the whole of his person in a mirror, the size of which is half of his own height.
  • The minimum size of the plane mirror required to be fixed on the wall of a room so that an observer at the centre of the room can see the full image of the wall behind him is one-third the height of the wall behind the observer.
  • The Angle of deviation (D) of a ray due to reflection at a plane mirror is twice the glancing angle (g). ie D=2g, where g= (90 degree-i) and i is the angle of incidence.
  • When a plane mirror is turned through an angle Theta, the direction of a light ray reflected from is changes 2Theta.
  • The principle of rotating mirror finds applications in the construction of several optical instruments and in devices like sextant, optical levers etc.
  • A set of two parallel mirrors, produces theoretically an infinite number of images. However, in practice only a limited number of images are observed, since each successive image is fainter than the last.
  • The total number of images formed by two plane mirrors inclined at right angles is 3.
  • The portion of the mirror from where reflection actually takes place is known as Aperture.
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