Question

Identify the portion between two wave crests or troughs:
$
  {\text{A}}{\text{. wave cycle}} \\
  {\text{B}}{\text{. amplitude}} \\
  {\text{C}}{\text{. frequency}} \\
  {\text{D}}{\text{. vibration}} \\
  {\text{E}}{\text{. speed}} \\
 $

Answer 1

- Hint: To do this question, one should know the meaning of the terms used in the question that are the crest and trough.

Complete step-by-step solution -
A crest is the apex point of the positive portion of a wave. It is the position where the particle has the maximum displacement.
 A trough is the bottom point of the negative portion of a wave. It is the position where the particle has a minimum displacement.

The portion between two crests and trough represents a wave cycle, since the same portion could then be used to generate the whole wave.
So, a cycle is just a small part, that describes the whole wave, and indicates its certain characteristics, like amplitude, wavelength, frequency etc.
A wave cycle is the collection of the maximums and the minimums.
There is no generalization to the number of maximums and minimums one wave cycle would contain. There are many ways to select a wave cycle. Like, the one having 2 crests and one trough as marked in the diagram above, or having 2 troughs and 1 crest. A wave cycle can also have 1 crest and 1 through each ( like a sine wave).

So, the correct option is (A).

Note: It is the distance between the two wave crests and troughs which is called the wavelength. Wavelength is a characteristic property while wave cycle is an imaging. In the question, it was asked about the portion, so the answer is a wave cycle.