Diffraction of water waves through a gap

Steps:

• Recall that diffraction occurs when waves encounter an obstacle or gap comparable to their wavelength, causing them to bend and spread.
• Visualize water waves approaching a barrier with a single gap: they should pass through and fan out circularly on the far side.
• Eliminate diagrams showing straight-line propagation (no bending) or reflection back toward the source.
• Select the diagram where waves curve outward symmetrically from the gap, matching Huygens' principle.

Why B is correct:

• Diagram B depicts waves spreading circularly from the gap, aligning with Huygens' principle that each point on a wavefront acts as a new wave source.

Why the others are wrong:

• A shows straight waves without spreading, ignoring diffraction bending.
• C illustrates reflection, with waves bouncing back from the barrier.
• D depicts refraction, with waves changing speed and direction unevenly.

Final answer: B