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Q.
The wave front due to a source situated at infinity is:
ManipalManipal 2005Wave Optics
Solution:
when you considered it a large distance and measuring justice Mall section of it then it can be considered to be plane wavefront source at Infinity
example the one coming from sun to earth surface is considered to be plain VU friend from light diverging from a point source will be spherical
So, the wave front due to a source situated at infinity is planar