Interference Pattern Variation

Steps:

• Waves interfere between points S and P, creating alternating bright and dark fringes.
• Detector Q moves slowly at constant speed, sampling signal amplitude at successive positions.
• Amplitude peaks at constructive interference (bright fringes) and minima at destructive (dark fringes).
• This results in regular oscillations in detected amplitude along the path.

Why B is correct:

• In wave interference, amplitude varies periodically with position due to phase differences, following the law of superposition.

Why the others are wrong:

• A: Amplitude oscillates, not a steady decrease.
• C: No net steady increase; pattern is symmetric and periodic.
• D: Interference causes variation, not constancy.

Final answer: B