Question 1
Multiple choiceMedium1 markThe graph shows the displacement of particles of a cord at one instant. The wave travels in the direction. Which row describes the particle motion and whether this wave can propagate through a vacuum?
| Particle motion relative to wave travel | Can propagate through a vacuum? | |
|---|---|---|
| A. | Parallel | Yes |
| B. | Parallel | No |
| C. | Perpendicular | No |
| D. | Perpendicular | Yes |
Show answer and explanation
Answer: C. The graph gives particle displacement along while the wave travels along therefore particle motion is perpendicular to the direction of travel. A wave that displaces particles of a cord is mechanical and requires a material medium, so it cannot propagate through a vacuum.
A: reads the horizontal position axis as the particle-motion direction and assumes the wave can travel without a medium.
B: reads the horizontal position axis as the particle-motion direction, giving parallel motion.
D: identifies the perpendicular motion correctly but mistakes a mechanical wave for one that can propagate through a vacuum.
Remember: mechanical waves require a medium; electromagnetic waves do not.