19. If you are watching a moving train, what would happen to the pitch of the whistle at a crossing as the locomotive approaches and then passes by the crossing?
a. The pitch would remain the same.
b. The pitch would increase suddenly as the train passed.
C. The pitch would decrease and then increase again.
d. The pitch would decrease suddenly as the train passed.

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