Diffraction of waves through a narrow gap

Steps:

• Identify the setup: plane waves approach a small gap in a barrier.
• Recall wave property: when wavelength is comparable to gap size, waves bend and spread.
• Apply diffraction principle: waves emerge as circular wavefronts from the gap acting as a new source.
• Confirm pattern: no straight propagation; spreading occurs perpendicular to original direction.

Why A is correct:

• A depicts circular waves radiating from the gap, matching Huygens' principle where each point on the wavefront acts as a secondary source.

Why the others are wrong:

• B shows straight-line continuation, ignoring diffraction bending.
• C illustrates multiple interference fringes, unsuitable for single-gap diffraction.
• D displays reflected waves bouncing back, not forward spreading.

Final answer: A