Fringe separation inversely proportional to slit separation

Steps:

• Fringe separation x given by x = λD / a, where λ is wavelength and D is screen distance.
• λ and D fixed, so x ∝ 1/a.
• As slit separation a increases, x decreases nonlinearly.
• Graph of x versus a is hyperbolic decay.

Why A is correct:

• Shows x decreasing inversely with a, matching double-slit interference formula x = λD / a.

Why the others are wrong:

• B: Linear increase implies direct proportionality, violating inverse relation.
• C: Constant x ignores dependence on a.
• D: x increasing with a contradicts formula.

Final answer: A