Explanation
In case of destructive interference (minima) phase difference is odd multiple of π
With white light, the rays reaching the centre has zero path difference. So we get white fringe at the centre and coloured near the central fringe.
Due to expansion of universe, the star will go away from the earth thereby increasing the observed wavelength. Therefore the spectrum will shift to the infrared region.
With reference to this theory the velocity of the observed is neglected w. r. t. the light velocity.
According to Doppler’s effect, wherever there is a relative motion between source and observer, the frequency observed is different from that given out by source.
Two beams having the same wavelength, monochromatic or white radiation, having the same initial phase (coherent source), can give interference pattern by superposition. But when their vibrations are perpendicular to each other, interference will not be possible.
Thickness of the film must be of the order of wavelength of light falling on film (i.e., visible light)
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