Frequency — Science definition

Defined in 2 courses:

Where it is taught

In use

What natural selection changes is the frequency of variants in a population — the proportion carrying each — not the individuals themselves.

Natural Selection, Adaptation & Population Change

Questions using frequency

Problem 1

Does a small frequency change alone prove selection?
Answer and explanation

No. Sampling, movement, and other processes may contribute; evidence about inheritance and reproductive success is needed.

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

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.

Problem 4

A source-position trace has peaks 0.2 s apart and swings from −3 to +3 mm around zero. Find period, frequency and amplitude, and distinguish amplitude from peak-to-trough span.
Answer and explanation

Period 0.2 s; frequency 5 Hz; amplitude 3 mm; peak-to-trough span 6 mm. The source moves locally rather than traveling across the sound path.

Use matching-peak separation for period and its reciprocal for frequency.

Measure amplitude from the middle position to a peak.

Period 0.2 s; frequency 5 Hz; amplitude 3 mm; peak-to-trough span 6 mm. The source moves locally rather than traveling across the sound path.

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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