- PRINCIPLE OF SUPERPOSITION
- WAVEFRONTS
- COHERENCE
- YOUNG’S DOUBLE SLIT EXPERIMENT (Y.D.S.E.)
- Analysis of Interference Pattern
- Fringe width
- Maximum order of Interference Fringes
- Intensity
- SHAPE OF INTERFERENCE FRINGES IN YDSE
- GEOMETRICAL PATH & OPTICAL PATH
- YDSE WITH OBLIQUE INCIDENCE
- THIN-FILM INTERFERENCE
- HUYGENS CONSTRUCTION
- REFLECTION AND REFRACTION
- REFLECTION AND REFRACTION

When two or more waves simultaneously pass through a point, the disturbance of the point is given by the

sum of the disturbances each wave would produce in absence of the other wave(s). In case of wave on

string disturbance means displacement, in case of sound wave it means pressure change, in case of

Electromagnetic Waves. it is electric field or magnetic field. Superposition of two light travelling in almost

same direction results in modification in the distribution of intensity of light in the region of superposition.

This phenomenon is called interference.

Read moreConsider a wave spreading out on the surface of water after a stone is thrown in. Every point on the surface

oscillates. At any time, a photograph of the surface would show circular rings on which the disturbance is

maximum. Clearly, all points on such a circle are oscillating in phase because they are at the same distance

from the source. Such a locus of points which oscillate in phase is an example of a wavefront

Read moreTwo sources which vibrate with a fixed phase difference between them are said to be

coherent. The phase differences between light coming form such sources does not

depend on time.

Read moreIn 1802 Thomas Young devised a method to produce a stationary interference pattern. This was based upon

division of a single wavefront into two; these two wavefronts acted as if they emanated from two sources having

a fixed phase relationship. Hence when they were allowed to interfere, stationary interference pattern was observed

Read moreWe have insured in the above arrangement that the light wave

passing through S1 is in phase with that passing through S

Read moreIt is the distance between two maxima of successive order on one side of the central maxima. This is

also equal to distance between two successive minima

Read moreMaximum order of Interference Fringes

Read moreSuppose the electric field components of the light waves arriving at point P(in the Figure : 3)

from the two slits S1 and S2 vary with time as

Read moreWe discuss the shape of fringes when two pinholes are used instead of the two slits in YDSE.

Fringes are locus of points which move in such a way that its path difference from the two slits remains constant

Read moreGEOMETRICAL PATH & OPTICAL PATH

Read moreYDSE WITH OBLIQUE INCIDENCE

Read moreIn YDSE we obtained two coherent source from a single

(incoherent) source by division of wave-front. Here we do

the same by division of Amplitude (into reflected and refracted

wave).

Read moreHuygens, the Dutch physicist and astronomer of the seventeenth century, gave a beautiful

geometrical description of wave propagation. We can guess that he must have

seen water waves many times in the canals of his native place Holland. A stick placed

in water and oscillated up and down becomes a source of waves. Since the surface of

water is two dimensional, the resulting wavefronts would be circles instead of spheres

Read moreWe can use a modified form of Huygens' construction to understand reflection and refraction of light. Figure

(10.2a) shows an incident wavefront which makes an angle ‘i’ with the surface separating two media, for example,

air and water. The phase speeds in the two media are v1 and v2. We can see that when the point A on the

incident wavefront strikes the surface, the point B still has to travel a distance BC = AC sin i, and this takes a

time t = BC/v1 = AC (sin i) / v1. After a time t, a secondary wavefront of radius v2t with A as centre would have

travelled into medium 2. The secondary wavefront with C as centre would have just started, i.e.. would have zero

radius. We also show a secondary wavelet originating from a point D in between A and C. Its radius is less than

v2t. The wavefront in medium 2 is thus a line passing through C and tangent to the circle centred on A. We can

Read morewhere n2 is the refractive index of medium 2 with respect to vacuum, also called the absolute refractive index of

the medium. A similar equation defines absolute refractive index n1 of the first medium. From Eq. we then get n21

Read more