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to produce interference pattern the sources should be coherent but two independent sources cannot produce such pattern. hence they won't produce interference fringes
two coherent light sources are produced by splitting a single light source
If they are not, the interference patterns become much more complicated, and vary over time.
Coherent sources are sources of light with a constant phase difference. The conditions for this are that there is a constant phase difference and that the light is of the same wavelength.
Constructive
to produce interference pattern the sources should be coherent but two independent sources cannot produce such pattern. hence they won't produce interference fringes
two coherent light sources are produced by splitting a single light source
If they are not, the interference patterns become much more complicated, and vary over time.
To make two coherent source for interference .Biprism make two sources.
A fresnel biprism is a triangular right prism with a highly obtuse angle in cross-section. The obtuse angle is near 180 degrees. The typical use of such a prism is to produce two coherent "virtual" light sources from one real point source. These virtual sources can be used to demonstrate interference.
For a steady interference pattern, the two sources of light must be monochromatic and coherent.The light coming from any star contains many wavelengths. Hence, it is not monochromatic.Also, the light is from two different sources. So, the two sources will not be coherent.Because of these reasons, the stars will not produce a stable interference pattern.
Coherent sources are sources of light with a constant phase difference. The conditions for this are that there is a constant phase difference and that the light is of the same wavelength.
Constructive
lasers
Young's experiment aimed at observing interference of light waves. To observe clear interference patterns it is necessary to use monochromatic sources. Using monochromatic sources are coherent with constant phase difference so the interference pattern remains same on screen with passage of time. But using just any source will give a changing phase difference and a changing interference pattern which is difficult to observe.
Diffraction is the spreading of waves that pass through a narrow opening or move past an obstacle ,whereas, interference is the phenomenon of redistribution of light in a medium as a result of light waves from two coherent sources.
Coherent sources are those that radiate waves with same phase or constant phase difference. They're very much essential for producing Fresnel's type of diffraction.