In this IIT physics video class we will be discussing wave optics. In the above physics video the following topics are going to be discussed. They are,

• wave front
• principle of least time
• Principle of super position.
• condition of sustained interference

The first person to support wave optics was Christian Huygens. He had described many phenomenons with his wave theory of light. The phenomenon’s were refraction, double refrection, etc. on the basis of wave front he described many phenomenon’s of light.  So what is the wave front theory?

If suppose you have thrown a stone in a still water. You can observe that, concentric circles are formed and each one moves away from the center. The entire particles in the center of the wave are in the same phase. And the envelope of these wave phases is known as wave front.  Further in the video we have discussed about it using diagrams which will help you understand this entire topic in a better wave. So what is wave front? Wave front is the locus of all particles in the same phase/ path/ envelope.

Properties of wave front:

• Every point in a wave front is a source of a new wavelength is originated in various directions in the forward direction. On this basis he had explained refraction and reflection. The wave front is in the form of concentric circles.
• The wave front moves forward and thus it becomes a new source of wavelengths. These new wavelengths are known as secondary wavelengths.
• The distance between two wavelengths is the product of speed of light and time tou required for moving from one point to another.

Further in this lecture for iit jee physics we have discussed principle of least time. This is one of the outcomes of the wave theory. This is beautifully explained in the video. The mathematical representation of principle of least time is,

Sin i/sin r =  μ = v1/v2

In jee physics lecture we have discussed about the principle of super position. According to this, if the displacement of a media point by some wave is supposed to be y1 and the displacement by the other particle at the same point be y2.

y1 = A1sinω1 t

y2 = A2sinω2 t

The resultant replacement is y1 + y2.

Y = A1sinω1 t + A2sinω2 t

The resultant displacement of a particle of a medium is vector sum of displacements caused by individual waves. Then we have discussed the condition of sustained interference. So what is interference?  Interference is defined as, “when the energy distributed by more than one identical source of light is modified due to superposition, a special pattern is observed. This special case off overlapping is known as interference.

Imagine if there are two light bulbs in your room and you can observe uniform light on the wall. If we use monochromatic lights instead, then we can observe alternate bright and dark fringes / areas. 