While aligning an optics demonstration, a teacher first projects a double-slit interference pattern on a screen 2.0m away using a 532nm green laser. The teacher then considers two separate modifications:
Modification 1 — Replace the green laser with a 650nm red laser while keeping all other conditions unchanged.
Modification 2 — Leave the green laser in place but move the screen so it is now 1.0m from the slits.
Assume the small-angle condition holds before and after each modification.
(a) For each modification separately, state whether the bright-to-bright fringe spacing Δy on the screen will increase, decrease, or remain the same compared with the original arrangement. Briefly explain your reasoning for each case.
(b) When both modifications are made simultaneously (red laser and1.0m screen distance), predict the net qualitative change in Δy relative to the original arrangement and justify your answer.
(c) Which single modification—changing the wavelength or changing the screen distance—produces the larger magnitude of change in Δy? Support your conclusion with conceptual reasoning based on proportional relationships.