Interference of light New

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Dr MAHESH SRIVASTAVA KV EOI KATHMANDU,NEPAL

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By: nomjb (14 month(s) ago)

A great way of presenting the concept of interference to the students

Presentation Transcript

INTERFERENCE OF LIGHT : 

Dr M. SRIVASTAVA K.V.EOI KTM INTERFERENCE OF LIGHT Presented By Dr MAHESH SRIVASTAVA Deptt Of Physics K.V. Embassy of India Kathmandu

SUPERPOSITION PRINCIPLE : 

Dr M. SRIVASTAVA K.V.EOI KTM SUPERPOSITION PRINCIPLE When two or more than two waves traveling through a medium and superimpose then they loose their individual identity and a resultant wave is formed, whose displacement is equal to the vector sum of the displacement of individual waves. Y= Y1+Y2+-------+Yn

INTERFERENCE OF LIGHT : 

Dr M. SRIVASTAVA K.V.EOI KTM INTERFERENCE OF LIGHT It is the phenomena of redistribution of light energy on account of superposition of light waves coming from the two coherent source of light The point at which intensity of light is maximum is called constructive interference. The point at which intensity of light is minimum is called destructive interference.

Constructive Interference : 

Dr M. SRIVASTAVA K.V.EOI KTM Constructive Interference Crest Resultant Wave Trough = Y t

Destructive Interference : 

Dr M. SRIVASTAVA K.V.EOI KTM Destructive Interference Crest Trough Resultant Wave = Y t

Interference Preconditions : 

Dr M. SRIVASTAVA K.V.EOI KTM Interference Preconditions Light must be monochromatic, i.e., involve just a single frequency and single wavelength. Light sources must be coherent, the relative phase is always the same. Light sources must have the same amplitudes. If these conditions do not hold, one still gets constructive and destructive interference but the interference pattern can change with time or not be complete (destructive interference leads to a decrease in amplitude but not to zero amplitude).

Producing Coherent Sources Sources of light waves which emits the light waves of same frequency, same wavelength and zero phase difference or constant phase difference are called coherent sources of light : 

Dr M. SRIVASTAVA K.V.EOI KTM Producing Coherent Sources Sources of light waves which emits the light waves of same frequency, same wavelength and zero phase difference or constant phase difference are called coherent sources of light Currently, it is much more common to use a laser as a coherent source The laser produces an intense, coherent, monochromatic beam over a width of several millimeters

Incoherent source : 

Dr M. SRIVASTAVA K.V.EOI KTM Incoherent source Two sources of light which do not emit light waves with a constant phase difference are called incoherent sources of light.

Slide 9: 

Dr M. SRIVASTAVA K.V.EOI KTM Young’s Double Slit Experiment (1802)

Young’s Double Slit Experiment : 

Dr M. SRIVASTAVA K.V.EOI KTM Young’s Double Slit Experiment L >>D and D>>λ

Slide 11: 

Dr M. SRIVASTAVA K.V.EOI KTM Young’s Double Slit Experiment

Experimental demonstration of Young’s double slit experiment : 

Dr M. SRIVASTAVA K.V.EOI KTM Experimental demonstration of Young’s double slit experiment

Experimental demonstration of Young’s double slit experiment : 

Dr M. SRIVASTAVA K.V.EOI KTM Experimental demonstration of Young’s double slit experiment

COHERENT SOURCES ON WATER SURFACE : 

Dr M. SRIVASTAVA K.V.EOI KTM COHERENT SOURCES ON WATER SURFACE

DOUBLE SLIT EXPERIMENTInterference of the waves on a water surface. : 

Dr M. SRIVASTAVA K.V.EOI KTM DOUBLE SLIT EXPERIMENTInterference of the waves on a water surface.

Interference : 

Dr M. SRIVASTAVA K.V.EOI KTM Interference Let’s say I have a speaker which emits sound with a wavelength of λ λ

Interference : 

Dr M. SRIVASTAVA K.V.EOI KTM Interference Now, I put another speaker behind the first speaker a distance D, and this speaker gives off sound at the exact same wavelength. What will someone hear some distance away from the speakers? λ λ D

Interference : 

Dr M. SRIVASTAVA K.V.EOI KTM If the distance D is equal to the wavelength of the sound, or any multiple of the wavelength, then the peaks of both sound waves will line up and constructive interference takes place. As a result, the sound gets louder (amplitude higher). Condition for constructive interference: D = nλ (n=1,2,3……) Interference λ D

Interference : 

Dr M. SRIVASTAVA K.V.EOI KTM If the distance D is equal to half the wavelength of the sound, or any multiple of half the wavelength, then the maxima of one sound wave will correspond to the minima of the second sound wave and destructive interference takes place. As a result, you will hear no sound!!! Condition for destructive interference: D = (n+1/2)λ (n=1,2,3……) Interference λ D

Resulting Interference Pattern : 

Dr M. SRIVASTAVA K.V.EOI KTM Resulting Interference Pattern The light from the two slits form a visible pattern on a screen The pattern consists of a series of bright and dark parallel bands called fringes Constructive interference occurs where a bright fringe occurs Destructive interference results in a dark fringe

Interference Patterns : 

Dr M. SRIVASTAVA K.V.EOI KTM Interference Patterns Constructive interference occurs at the center point The two waves travel the same distance Therefore, they arrive in phase

Interference Patterns, 2 : 

Dr M. SRIVASTAVA K.V.EOI KTM Interference Patterns, 2 The lower wave has to travel farther than the upper wave The lower wave travels one wavelength farther Therefore, the waves arrive in phase A bright fringe occurs

Interference Patterns, 3 : 

Dr M. SRIVASTAVA K.V.EOI KTM Interference Patterns, 3 The lower wave travels one-half of a wavelength farther than the upper wave The trough of the bottom wave overlaps the crest of the upper wave This is destructive interference A dark fringe occurs

Uses for Young’s Double Slit Experiment : 

Dr M. SRIVASTAVA K.V.EOI KTM Uses for Young’s Double Slit Experiment Young’s Double Slit Experiment provides a method for measuring wavelength of the light This experiment gave the wave model of light a great deal of credibility It is inconceivable that particles of light could cancel each other

THANK YOU : 

Dr M. SRIVASTAVA K.V.EOI KTM THANK YOU