10 11) we will not observe any interference fringes This is because of the fact that the light wave emitted
from an ordinary source (like a sodium lamp) undergoes
abrupt phase changes in times of the order of 10–10
seconds 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