Question

Sawyer is studying diffraction. He draws a diagram of a plane wave to show how light waves travel.

Transverse waves with the crests being wavefronts with lines of wavefronts moving toward the right and an arrow showing the direction of movement.
Which best describes Sawyer’s error?

The wave fronts should be perpendicular to the direction in which the waves move.
The arrow showing the direction of movement of the waves should be pointing to the left.
The arrow showing the direction of movement of the waves should be pointing downward.
The wave fronts should be both parallel and perpendicular to the direction in which the waves move.

Answer 1

The wave fronts should be perpendicular to the direction in which the waves move.

Explanation: For a plane wave, wavefronts (surfaces of constant phase/crests) are perpendicular to the propagation direction (rays), not parallel.