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• Reflection: Light falling on an object bounces back
• Ray of light: It is a very fine beam of light
• Incident ray: Ray that strikes on the surface is called incident ray
• Reflected ray: Ray that bounces back from the surface, or the ray which comes from the surface after reflection is called reflected ray
• Normal: Line perpendicular to the surface of mirror at the point of intersection of incident and reflected ray is a normal.
• Angle of incidence (∠i): Angle made by incident ray with the normal
• Angle of reflection (∠r): Angle made by reflecting ray with the normal
• Laws of reflection:
  • The angle of incidence is always equal to the angle of reflection.
  • The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
• Image formation by plane mirrors:
  

  Nature of image	Virtual and erect
  Size of image	Same as that of object

Click here to watch video on Image Formation By Plane Mirrors

• Plane mirrors show lateral inversion: Left appears right and right appears left
• Regular reflection: In this reflection, reflected rays are parallel. Such reflection occurs on smooth and regular surface.
• Diffused reflection: In this reflection, reflected rays are in different directions. Such reflections occurs on surfaces with irregularities.
• Laws of reflection is obeyed by regular as well as diffused reflection.
• Using the combination of mirrors, number of images can be formed by the formula,
  n= 360°/θ -1
  n = number of images, θ = angle between the mirrors
• Kaleidoscope: Device used to make beautiful appearing patterns using the principle of multiple image formed by mirrors placed at an angle.

Click here to watch video on How To Make A Kaleidoscope?

• Dispersion: Splitting of light in its different colors. E.g Rainbow is an example of dispersion
• Working of human eye:
  • Cornea: Thin membrane of human eye.
  • Iris: Dark muscular diaphragm behind the cornea.
  • Pupil: Small opening at the centre of the iris. It controls the amount of light entering our eyes.
  • Eyeball: Spherical shape of diameter about 2.3 cm
  • Lens: Crystalline lens behind the pupil. Provides fine adjustment of focal length.
  • Retina: Image is formed on retina. When light falls on retina, light sensitive cells gets activated and generates electric signals, which are passed to brain via optic nerve
• Functioning of lens:
  

  	Size of lens	Change in focal length
  Normal vision	Eye is relaxed	2.5 cm
  Distance vision	Decreases	Increases
  Near vision	Increases	Decreases

  • Power of accommodation : Ability of lens to adjust itself in order to form a clear image on the retina.
  • Distance of distinct vision (D): Normal vision in which object can be seen clearly without strain on eyes. For normal human eye it is 25 cm
• How to take care of eyes?
  • Consult a doctor even for minor vision problems
  • Make use of spectacles with doctors suggestion
  • If dust particles enter in the eyes, wash it with clean water
  • Take a balanced diet
  • Include food sources containing vitamin A, like carrots, broccoli, vegetables and cod liver oil, milk, curd, cheese, butter, papaya, mango, etc.
• Visually challenged person can read and write as using optical and non optical aids
  • Optical aids: Bifocal lenses, tinted lenses, contact lenses, magnifiers and telescopic aids.
  • Non optical aids: Braille writer slate and stylus, cassettes, tape recorders, talking books, etc.