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प्रश्न
Why are multiple colours observed over a thin film of oil floating on water? Explain with the help of a diagram.
उत्तर
Interference due to a thin film:
The brilliant colours of soap bubbles and thin films on the surface of water are due to the interference of light waves reflected from the upper and lower surfaces of the film. The two rays have a path difference which depends on the point on the film that is being viewed. This is shown in above figure.
The incident wave gets partially reflected from upper surface as shown by ray AE. The rest of the light gets refracted and travels along AB. At B it again gets partially reflected and travels along BC. At Cit refracts into air and travels along CF. The parallel rays AE and CF have a phase difference due to their different path lengths in different media. As can be seen from the figure, the phase difference depends on the angle of incidence θ1, i.e., the angle of incidence at the top surface which is the angle of viewing, and also on the wavelength of the light as the refractive index of the material of the thin film depends on it. The two waves propagating along AE and CF interfere producing maxima and minima for different colours at different angles of viewing. One sees different colours when the film is viewed at different angles.
As the reflection is from the denser boundary, there is an additional phase difference of π radians (or an additional path difference λ). This should be taken into account for mathematical analysis.
संबंधित प्रश्न
A narrow slit S transmitting light of wavelength λ is placed a distance d above a large plane mirror, as shown in the following figure. The light coming directly from the slit and that coming after the reflection interfere at a screen ∑ placed at a distance D from the slit. (a) What will be the intensity at a point just above the mirror, i.e. just above O? (b) At what distance from O does the first maximum occur?
A long narrow horizontal slit is paced 1 mm above a horizontal plane mirror. The interference between the light coming directly from the slit and that after reflection is seen on a screen 1.0 m away from the slit. Find the fringe-width if the light used has a wavelength of 700 nm.
Answer in brief:
Explain what is the optical path length. How is it different from actual path length?
Answer in brief:
What is meant by coherent sources?
Explain constructive and destructive interference with the help of a diagram?
How does wavefront division provide coherent sources?
Obtain the equation for bandwidth in Young’s double slit experiment.
Two independent monochromatic sources cannot act as coherent sources, why?
In Young’s double-slit experiment, 62 fringes are seen in the visible region for sodium light of wavelength 5893 Å. If violet light of wavelength 4359 Å is used in place of sodium light, then what is the number of fringes seen?
The ratio of maximum and minimum intensities in an interference pattern is 36 : 1. What is the ratio of the amplitudes of the two interfering waves?
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If the monochromatic source in Young's double slit experiment is white light, then ____________.
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In Young's experiment, the distance between the slits is doubled and the distance between the slit and screen is reduced to half, then the fringe width ____________.
In Young's double slit experiment the source is white light. One slit is covered with red filter and the other with blue filter. There shall be ____________.
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In Young's double-slit experiment, the distance between the slits is 3 mm and the slits are 2 m away from the screen. Two interference patterns can be obtained on the screen due to light of wavelength 480 nm and 600 run respectively. The separation on the screen between the 5th order bright fringes on the two interference patterns is ______
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If we have two coherent sources S1 and S2 vibrating in phase, then for an arbitrary point P constructive interference is observed whenever the path difference is ______.
What is meant by Constructive interference?
A beam of electrons is used in Young's double-slit experiment. If the speed of electrons is increased then the fringe width will ______.
The interference pattern is obtained with two coherent light sources of intensity ratio 4 : 1. And the ratio `("I"_"max" - "I"_"min")/("I"_"max" + "I"_"min")` is `5/x`. Then the value of x will be equal to ______.
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