Thus the light waves coming out from two
independent sources of light will not have any fixed
phase relationship and would be incoherent, when this
happens, as discussed in the previous section, the
intensities on the screen will add up The British physicist Thomas Young used an
ingenious technique to “lock” the phases of the waves
emanating from S1 and S2 He made two pinholes S1
and S2 (very close to each other) on an opaque screen [Fig 10