Concepts of Optics: Quick Revision of Formulae for IIT JEE, UPSEE & WBJEE

Find important formulae from the unit Concepts of Optics for quick revision. These formulae will prove very helpful during at the time of the examination.


Updated: Dec 21, 2016 17:16 IST


Find important formulae from the unit Concepts of Optics for quick revision. This unit contributes about 10 percent of total questions in any entrance examinations.
When exams are round the corner then it is not possible to revise complete books so we have come up with unit wise formulae and important terms. Once you have gone through chapters thoroughly and understood it well there is no need to study it again and again. You can only revise important formulas and terms which will save your precious time.

In this regard find Concepts of Optics important Formulae for Quick Revision. These formulae will be helpful in various engineering entrance examinations. In UPSEE and WBJEE where most of questions are asked directly on formulae, this quick revision note is very important.

Concepts of Optics


  • The  incident  ray,  reflected  ray and  the  normal  to  the  reflecting  surface  lie in  the  same  plane.


  • The Cartesian sign convention tells us which distance should be taken positive and which should be taken negative.



             where, f = focal length, R = radius of curvature

  • The mirror equation is given as:


         where, u = Distance of object from pole, v = distance of image from pole

          f = Focal length, R = Radius of curvature

  • The magnification (m) is given as:


         where, m = magnification (or linear magnification ), I = size of image, O = Size of object

Laws of Refraction

  • The incident ray, the refracted ray and the normal  to  the  interface  at  the  point  of incidence, all lie in the same plane.
  • The ratio of the sine of the angle of incidence to the sine of angle of refraction is constant. Remember that the angles of incidence (i ) and refraction (r ) are the angles that the incident and  its refracted ray make with the normal, respectively.



 Total Internal Reflection:


              where, C = critical angle

  • Critical angle depends upon wavelength of light as: Mathematically,


  • The thin lens formula is given as


  • The magnification m for the lens is given as:


         where, m = magnification (or linear magnification ), I = size of image, O = Size of object

  • The power of a lens is given by:


  • The SI unit for power of a lens is dioptre (D).

Combination of lens

  • Combination will behave as a lens, which have more power or lesser focal length.


  • For a system of lenses, the net power is given as:

           P = P1 + P2 + P3

  • For a system of lenses, the net magnification is given as:

           m = m1 × m2 × m3 ×…

UPSEE 2017 Solved Sample Paper Set-1

Refraction through a Prism


  • A = r1 + r2

          where, A is the angle of the prism

  • δ = (μ - 1)A

           where, δ is deviation through prism

  • When refracted ray inside the prism is parallel to the base of the prism, then


           δm is minimum deviation

For Young’s double slit experiment:


  • Path difference


  • For constructive interference


  • For destructive interference


  • Fringe width(w)


  • nth order maxima or bright fringe


  • nth order minima or dark fringe


  • Fringe shift due to a glass slab in path of one of the slits


  • Ratio of maximum intensity and minimum intensity in the interference is given as:


  • If two individual intensities at any point A is assume to be same (I0), then the resultant intensity at A is given as:




Modern Physics: Quick Revision of Formulae for IIT JEE, UPSEE and WBJEE

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