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Reflection of light Notes for Class 10



Introduction

  • Light is a form of energy due to which we are able to see the objects which emits light for example objects like sun, lamp, candle emits light of their own and thus they are known as luminous objects.
  • There are objects like table , chair etc. which are not luminous objects and still we are able to see them and this happens because they reflects lights which falls on them from a luminous object like sun, lamp etc. and when this reflected light reaches our eyes we are able to see such non luminous objects.
  • Light rays basically consist of electromagnetic waves which do not require any material medium (like solid, liquid or gas) for their propagation.
  • The wavelength of visible light waves is very small and is of the order of \(4 \times {10^{ - 7}}m\) to \(8 \times {10^{ - 7}}m\) .
  • Speed of light waves depends on the medium through which they pass as speed of light in air is slightly less than the speed of light in vacuum \(8 \times {10^{ 8}}m/s \) same way speed of light in water and glass is much less than that in air.
  • When light falls on the surface of an object it can either be
    1. Absorbed:- If an object absorbs all the light falling on it , then it will appear perfectly black for example a blackboard
    2. Transmitted: - An object is said to transmit light if it allows light to pass through itself and such objects are transparent.
    3. Reflected:- If an object sends back light rays falling on its surface then it is said to have reflected the light

Reflection of Light

  • The process of sending back light rays which falls on the surface of an object is called REFLECTION of light
  • Silver metal is one of the best reflectors of light.
  • Mirrors we use on our dressing tables in our home are plane mirrors.
  • A ray of light is the straight line along which the light travelled and a bundle of light rays is called a beam of light.
  • Laws of Reflection of light
    1. The angle of incidence is equal to the angle of reflection, and
    2. The incident ray, the reflected ray and the normal to the mirror at the point of incidence all lie in the same plane.
  • These laws of reflection are applicable to all types of reflecting surfaces including spherical surfaces

Real and Virtual images

  • An image is formed when the light rays coming from an object meet at a point after reflection from a mirror (or refraction from lens).
  • The images are of two types
    1. Real Images:- Real images are formed when rays of light that comes from an object (or source) meets at a point after reflection from a mirror (or refraction from a lens). Real images can be formed on a screen and can be seen with the eyes.
    2. Virtual images:- Virtual image is an image in which the outgoing rays from an object do not meet at a point. It will appear to meet at a point in or behind the optical device (i.e., a mirror) but they do not actually meet after reflection from a mirror (or refraction from a lens). A plane mirror always forms virtual images.
  • Characteristics of images formed by mirrors:-

    (a) Images formed by mirrors are always virtual and erect
    (b) Size of image is always equal to the size of the object and the image is laterally inverted.
    (c) The images formed by the plane mirror are as far behind the mirror as the object in front of the mirror.
  • Lateral inversion:- If an object is placed in front of the mirror, then the right side of the object appears to be the left side and left side of the object appears to be the right side of this image. This change of sides of an object and its mirror image is called lateral inversion.


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