Rectilinear propagation of light

[Vivek98phyboy]

How is it possible for different parts of a single rectangular wavefront to produce different intensity at particular point(P) despite the fact that wavefront is something which has all the particles at same phase?

 

[ZapperZ]

Can't you apply Huygens's principle here?

Secondly, this does not mean that different points will have different intensity. After all, one can perform this same type of analysis everywhere on the plane of the wavefront. They will all add to the same intensity (ignoring edge effects), because each point on the "screen" will have the same "cone" from all the different wavelets.

Zz.