Interference of light presentation
- 1. Interference of lightInterference of light 1B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 2. Interference is the superposition of two or more waves resulting in the modification of the wave intensity. Interference will be sustained if it is by two or more coherent waves of same frequency. Interference resulting in minimum intensity is known as destructive interference. Interference resulting in maximum intensity is known as constructive interference. 2B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 3. Nature of Interference depends on the path difference or phase difference between the interfering waves. constructive interference. integral multiple of wavelength δ = nλ (Phase difference φ= 2nπ) Path difference is 3B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 4. Nature of Interference depends on the path difference or phase difference between the interfering waves. destructive interference. Path difference is Odd integral multiple of half of the wavelength δ = (2n+1)λ/2 (Phase difference φ= (2n+1)π) Path difference is 4B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 5. 1. Interfering light waves should be of same frequency. 2. The two sources must be coherent. 3. Interfering light waves should travel Conditions for SUSTAINED interference pattern. 3. Interfering light waves should travel almost in the same direction. 4. Interfering light waves should be of almost same amplitude. 5. The two sources producing the coherent light must be narrow. 5B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 6. Each slit acts as an independent source of waves. YOUNG’S DOUBLE SLIT EXPERIMENT Waves from each slit interfere constructively or destructively at the screen producing dark or bright bands. 6B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 7. YOUNG’S DOUBLE SLIT EXPERIMENT: Theory 7B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 8. YOUNG’S DOUBLE SLIT EXPERIMENT: Theory For P to be a bright point constructive interference should take place. d sin θ= n λ. since sin θ= x/D xd/D= n λ or x= n λD/dxd/D= n λ or x= n λD/d the next bright point is x′= (n+1) λD/d distance between two successive bright spots( fringes) is x′–x=β width between two successive bright fringes is β= λD/d 8B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 9. YOUNG’S DOUBLE SLIT EXPERIMENT: Theory For P to be a dark point destructive interference should take place. d sin θ= (2n+1) λ/2. since sin θ= x/D xd/D= (n+1/2) λ or x= (n+1/2) λD/dxd/D= (n+1/2) λ or x= (n+1/2) λD/d next dark point is x′= (n+1+1/2) λD/d distance between two successive bright spots( fringes) is x′–x=β width between two successive dark fringes is β= λD/d 9B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 10. YOUNG’S DOUBLE SLIT EXPERIMENT: Theory Width between two successive bright fringes or dark fringes is same β= λD/d bright and dark fringesbright and dark fringes are separated by equal distance. B D B D B D B D B 10B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 11. : . Coherent sources If two light sources emitting light waves with the same phase or having a constant phase difference are called coherent sources. Two light sources are said to be coherent if they emit light waves of the same frequency with same phase or a constant phase difference. 11B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 12. : . Coherent sources Two independent sources cannot emit light with constant phase difference as their emission is extremely random. Thus they can not be coherent sources NOTE: Thus they can not be coherent sources coherent sources from a single source are obtained in two distinct ways. 12B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 13. : . 1. Coherent sources by division of wavefront: In this method wavefront of a light source is divided into two or more parts through refraction. Light passing through a biprism can produce two virtual images. The two virtual images act as coherent sources. Example: 13B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 14. 1. Coherent sources by division of wavefront: Light coming from S1 and S2 are coherent 14B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 15. 2. Coherent sources by division of amplitude In this method wavefront of a light source is subjected to partial reflection and partial refraction. :Light reflected by a thin film or refracted through a transparent thin film. We have here two sets of wavefronts moving in the same direction travelling in phase. Example: 15B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 16. 2. Coherent sources by division of amplitude Reflected waves are coherent Refracted waves are coherent 16B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru
- 17. 1.Interference is the property of B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 17 Longitudinal waves only •Transverse waves only •Both Longitudinal and transverse waves
- 18. 2.Interference of two waves can happen when B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 18 •The two waves are monochromatic •The two waves are coherent •neither of the above conditions are satisfied
- 19. 3.Coherent sources will have B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 19 •Zero phase difference •constant phase difference •any of the above
- 20. 4.Two atoms of the sodium vapour source emitting light waves B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 20 •can never be coherent •can be coherent always •can be coherent only at a given instant
- 21. 5.The constructive interference of two monochromatic light waves depends on B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 21 •Path difference between the waves •Amplitude of the waves •frequency of the waves
- 22. 6.The destructive interference of two monochromatic light waves depends on B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 22 •Phase difference between the waves •Intensity of the waves •Wavelength of the waves
- 23. 7.If mercury light is used instead of sodium light in a Young's double slit experiment B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 23 •Screen will be dark •Screen will be bright •Coloured fringes will appear with central bright fringe
- 24. 8.fringe width in an Interference pattern with a monochromatic source due a double slit depends B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 24 Directly on the wavelength and inversely on slit separation •Directly on the slit separation and inversely on wavelength •Directly on the slit separation and wavelength
- 25. 9. Example of obtaining coherent sources by division of wavefront is B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 25 •Biprism •Light refracted through a thin transparent film •None of the above
- 26. 10.Example of obtaining coherent sources by division of amplitude is B.V.Sreedhara Swamy,Department of Physics,National College, Jayanagar, Bengaluru 26 •Biprism •Light reflected from a thin film •None of the above