Which of the following correctly describes what is meant by a medium of wave travel? (A) A medium of wave travel is the midpoint of a traveling wave. (B) A medium of wave travel is the average speed that a wave travels at. (C) A medium of wave travel is the average amplitude of a traveling wave. (D) A medium of wave travel is the position of a traveling wave when it is at the midpoint between its origin and its destination. (E) A medium of wave travel is a substance that a wave travels through.
In this question, we’re talking about wave travel. So, let’s briefly recall some of the key features of transverse and longitudinal waves. Transverse waves, like one created by shaking a rope up and down, oscillate perpendicular to the direction of propagation, or the direction that the wave as a whole is traveling. On the other hand, longitudinal waves such as a sound wave traveling through air oscillate parallel to the direction of propagation.
Remember, all waves travel without a net transfer of matter. For example, in the case of a wave in a rope, the rope itself doesn’t actually move sideways; it just wiggles around some. Still though most waves do require matter to carry energy for them. For the examples below, the transverse wave travels by means of a rope, and the longitudinal wave travels by means of air particles. The stuff that a wave travels by means of is known as the wave’s medium.
Now, let’s look at our answer options. Both (A) and (D) define the medium as a location or a point in space, specifically some midpoint, either on the wave or somewhere in its path. But let’s not confuse the words medium and midpoint. Although in some contexts medium is used to mean intermediate or midway, within the context of wave travel medium refers to the stuff that carries a wave’s energy, not a point somewhere in space. Let’s eliminate (A) and (D).
Next, notice that the definitions given by options (B) and (C) also rely on a word that sometimes used as a synonym of the word medium, that is, average. This tricky wording might be tempting, but still option (B) is referring to a speed and (C) is referring to an amplitude. While it is true that speed and amplitude are important features of a wave, they are not what is meant by the phrase “a medium of wave travel.” Let’s eliminate these two choices as well.
Finally, option (E) says it’s the substance that a wave travels through. This agrees with our understanding of a medium as the stuff that a wave travels by means of, such as rope or air particles or water in the ocean. Therefore, answer choice (E) is correct. A medium of wave travel is a substance that a wave travels through.