A physics class investigates double-slit interference using three different experimental setups. Each setup employs monochromatic light, two narrow parallel slits, and a flat viewing screen that is perpendicular to the beam. The only quantities that differ among the setups are the wavelength of the light λ, the center-to-center slit separation d, and the distance L from the slits to the viewing screen.
Setups
• Setup A: λ=600nm, d=0.30mm, L=1.0m
• Setup B: λ=480nm, d=0.20mm, L=1.0m
• Setup C: λ=600nm, d=0.30mm, L=1.5m
Bright-to-bright (or dark-to-dark) spacing Δy is defined as the distance between two adjacent bright (or dark) interference fringes measured on the viewing screen at points close to the center of the pattern.
Assume small-angle conditions are satisfied for all three setups.
(a) Rank the three setups from largest Δy to smallest Δy. Clearly indicate any ties.
(b) Provide a qualitative justification for your ranking by referring to how each relevant parameter affects Δy. Do not perform a numerical calculation.
(c) Between Setups A and B, suppose the experimenter is allowed to change exactly one quantity—either the light’s wavelength, the slit separation, or the screen distance—while keeping the other two quantities fixed at their original values for each setup. Identify which single change would result in the greatest percentage increase in Δy relative to the original spacing in that setup, and justify your choice qualitatively.