Amplitude — Science definition

Defined in 3 courses:

Where it is taught

In use

Amplitude is the height of the wave measured from its rest position up to a crest (its peak).

Wave Properties

In simple small-amplitude models, medium particles oscillate locally rather than traveling the entire propagation distance.

Wave Properties

Questions using amplitude

Problem 1

What is B’s amplitude and what quantity remains unchanged?
Answer and explanation

Amplitude is 3 mm. The cycle count per time, and hence frequency of 200 Hz, is unchanged in this comparison.

Amplitude is 3 mm. The cycle count per time, and hence frequency of 200 Hz, is unchanged in this comparison.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 2

Illustrative sources A/B/C have amplitudes 1/3/1 mm and complete 4/4/6 cycles respectively in 0.02 s. Compare frequency and amplitude and explain what a receiver prediction would need.
Answer and explanation

A and B are 200 Hz, while C is 300 Hz. B has three times A’s amplitude; C has A’s amplitude but higher frequency. Frequency and amplitude are distinct. Predicting received sound also needs distance, medium, losses and receiver response. The source records alone do not establish an exact perceived loudness.

A and B are 200 Hz, while C is 300 Hz. B has three times A’s amplitude; C has A’s amplitude but higher frequency. Frequency and amplitude are distinct. Predicting received sound also needs distance, medium, losses and receiver response. The source records alone do not establish an exact perceived loudness.

Response criteria

  • Use the supplied conditions and relevant evidence.
  • Explain the scientific mechanism or calculation.
  • State a meaningful limitation or testable next step.

Problem 3

A source completes 8 cycles in 0.04 s at amplitude 2 mm. Another completes 8 cycles over the same time at 4 mm. Compare the changed quantity and a limit of predicting what a person hears.
Hints

Distinguish the observed quantities, the proposed mechanism and its conditions.

Answer and explanation

Both have frequency 200 Hz; amplitude doubles. Frequency-related pitch is comparable in the simple model, while received loudness also depends on distance, medium and receiver. The amplitude comparison alone does not fix a person’s perception.

Both have frequency 200 Hz; amplitude doubles. Frequency-related pitch is comparable in the simple model, while received loudness also depends on distance, medium and receiver. The amplitude comparison alone does not fix a person’s perception.

Problem 4

Change vibration size without changing cycle rateChange vibration size without changing cycle rateSmaller displacement amplitudeLarger displacement amplitudeSame time window; both complete two cycles.
Both source-position records show two cycles during the same stated time window, with different displacement amplitudes. Amplitude is measured from the middle position to a peak, not from peak to trough. The sketches compare patterns qualitatively; an actual amplitude and frequency require numerical axis scales, as in the OpenSciEd graphs used below.
For this unit’s illustrated case, which record has a higher frequency? What quantity differs, and what additional labels are needed for a numerical amplitude?
Answer and explanation

Neither has a higher frequency in this matched window. Displacement amplitude differs; a numerical vertical position scale and units are needed to measure it.

A cycle is one complete repeat, such as one peak to the next matching peak. A taller trace does not automatically have more cycles. Compare amplitude and frequency one at a time rather than using the word louder for both.

Neither has a higher frequency in this matched window. Displacement amplitude differs; a numerical vertical position scale and units are needed to measure it.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

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