Wavefront Properties for Point Sources

Steps:

• Wavefronts are surfaces connecting points of equal phase in a wave.
• For a point source in two dimensions, wavefronts expand as concentric circles centered on the source.
• Rays, indicating energy propagation direction, are radial lines from the source.
• Wavefronts remain perpendicular to these rays everywhere.

Why D is correct:

• Huygens' principle defines wavefronts from a point source as circular and perpendicular to the propagation direction (rays).

Why the others are wrong:

• A: Statement 1 is false; point source wavefronts are curved, not straight lines.
• B: Statement 1 is false; wavefronts are circular, not straight.
• C: Statement 3 is false; wavefronts are perpendicular, not parallel, to energy flow.

Final answer: D