Which of the following statements is correct?
a. coherent sources are not needed to produce interference fringes
b. two coherent light sources do not always produce bright and totally dark fringes on a screen
c. the atoms in a tungsten filament lamp produce coherent light waves
d. the yellow light from a street lamp is coherent light
The Attempt at a Solution
(a) is wrong because coherent sources are needed to produce interference fringes
(c) is wrong because the movement of atoms is random hence the light waves produced are not coherent
(d) is wrong (same reason as (c))
So only option (b) is left. But I also think it is wrong because if coherent sources are needed to produce interference pattern, does it also mean that two coherent sources will always produce interference pattern (bright and dark fringe)?