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a
shape of source
b
distance of source
c
both 1 and 2
d
none of the above
answer is C.
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Detailed Solution
For a point source of light, wave fronts at finite distance are concentric spherical surfaces.For a long line source of light, wave fronts at finite distances are co-axial cylindrical surfaces.For parallel rays of light wave fronts are plane surfaces.At very large distance rays of light, emerging from any sources, become nearly parallel.So option - (3) is right.