Main Points


  • When a ray of light falls on a shiny surface, it bounces back. This phenomenon is called reflection of light.
  • Nature of image in plane mirror: Image is virtual, erect and is laterally inverted. Image distance is equal to object distance.
  • In most of the cases, a concave mirror makes real and inverted image.
  • A convex mirror always makes a virtual and erect image.
  • A convex lens makes real and inverted image in most of the cases.
  • A concave lens always makes virtual and erect image.
  • The set of sign conventions to measure various distances with reference to mirrors is called New Cartesian Sign Convention.
  • Object distance is always taken as negative and image height is always taken as positive.
  • Mirror formula gives the relation between object distance (u), image distance (v) and focal length (f).
  • The extent to which an image is enlarged or diminished with reference to object size is called magnification.
  • When a ray of light travels opaquely from one medium to another, it experiences some deflection in its path. This phenomenon is called refraction of light.
  • When a ray of light travels from a rarer medium into a denser medium it bends towards the normal. When a ray of light travels from a denser medium into a rarer medium it bends away from the normal.
  • The ratio sine of angle of incidence to sine of angle of refraction is constant for the given pair of media and for the light of a given colour.
  • Absolute Refractive Index: When refractive index of a medium is taken with reference to vacuum or air then it is called absolute refractive index.
  • A transparent medium bound by two surface out of which at least one surface is spherical is called lens.
  • When rays of light from infinity pass through a convex lens; all of them converge at a point. Due to this, a convex lens is also called a converging lens.
  • When rays of light from infinity pass through a concave lens; all of them appear to diverge from a single point. Due to this, a concave lens is also called a diverging lens.
  • The reciprocal of focal length is called the power of a lens. The SI unit of power of lens is diopter (D).

These main points are highly helpful for last minute preparation for examination. You can glance through them while going for examination. You can view them in the school bus, in car, in elevator, etc.