Ch – 10 Light (Reflection)

Important Notes:

  • If an opaque object on the path of light becomes very small, light has a tendency to bend around it and not walk in a straight line. Then this effect is known as “Diffraction of light“.
  • Laws of reflection of light are –
    • The angle of incidence is equal to the angle of reflection.
    • The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
  • Properties of image formed by a Plane mirror –
    • Image is erect & virtual
    • Size of image = Size of object
    • Image formed is as far behind the mirror as the object is in front of it
    • Image is laterally inverted
  • Most common type of curved mirror is spherical mirror.
  • The mirrors whose reflecting surfaces are spherical are called “Spherical Mirror“.
  • A spherical mirror whose reflecting surface is curved inwards is called “Concave Mirror“.
  • A spherical mirror whose reflecting surface is curved outwards is called “Convex Mirror“.
  • The centre of the reflecting surface of a spherical mirror is called “Pole“. It is represented by the letter P.
  • The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre, which is known as “Centre of Curvature of Spherical Mirror“. It is represented by letter C.
  • The centre of curvature in concave mirror lies in front of it while in convex mirror it lies behind the mirror.
  • The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the “Radius of Curvature of Mirror“. It is represented by the letter R.
  • A straight line passing through the pole and the centre of curvature of a spherical mirror is known as “Principal Axis“.
  • The diameter of the reflecting surface of a spherical mirror is called its “Aperture“.
  • The distance between the pole and the principal focus of a spherical mirror is called the “Focal Length“. It is represented by the letter f.
  • For small spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length i.e. R = 2f.
  • The point where a beam of light parallel to the principal axis appears to diverge or converge from a point on principal axis is known as “Principal Focus“. It is represented by the letter F.
  • The image formed by a concave mirror depends on the position of the object in relation to points P, F and C.
  • Concave mirrors are commonly used in torches, search-lights and vehicle-headlights.
  • Convex mirrors are commonly used as rear view mirrors in vehicles.
  • The distance of the object from its pole is called the “Object Distance (u)“.
  • The distance of the image from the pole of the mirror is called the “Image Distance (v)“.
  • The distance of the principal focus from the pole is called the “Focal Length (f)“.
  • Mirror formula is 1/v + 1/u = 1/f.
  • Magnification is expressed as the ratio of the height of the image to the height of the object.

Published by Priya Prakash

In the midst of winter, i found there was within me an invincible summer ~ Albert Camus

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