Sound diffracts through the open doorway

Steps:

• Sound waves from the bell travel in straight lines but encounter the closed door, blocking most entry to the room.
• With the door closed, only faint sound reaches the student via diffraction around edges or walls.
• Opening the door creates a wider aperture, allowing more waves to diffract and bend into the room.
• Increased wave amplitude at point X makes the sound louder.

Why A is correct:

• Diffraction is the bending and spreading of waves around obstacles or through openings, enabling sound to enter the room more effectively when the door opens.

Why the others are wrong:

• B: Reflection involves waves bouncing off surfaces like walls, which doesn't explain sound entering through the doorway.
• C: Refraction is the bending of waves due to speed changes in different media, not applicable to air or door openings here.
• D: Option incomplete and irrelevant to the scenario.

Final answer: A