Ray Says That Interference Effects Cannot Be Observed with Visible

Multiple Choice

Ray says that interference effects cannot be observed with visible light because random phase changes occur in time intervals less than a nanosecond. Stacy says that doesn't matter if collimated light from a single source reaches multiple openings. (They are arguing about a light source 50.0 cm away from two 0.0100-mm-wide slits, 2.00 mm apart, with a screen 1.00 m away from the slits.) Which one, if either, is correct, and why?

A) Ray, because the phases at the two slits will be random and different.
B) Ray, because it takes light over 3 ns to travel 1.00 m to the screen.
C) Stacy, because the difference in time of travel from the source to the slits is no more than about 7 × 10−12 s.
D) Stacy, but only if a lens is placed in front of the slits.
E) Both, because interference of light never occurs outside a physics lab.