Not given in the exam, recall it.
What it is for
Period and frequency is used in Waves (SPM Physics Form 4). Keep the SI units in every line of working. Waves
Symbols and SI units
| Symbol | Meaning | SI unit |
|---|---|---|
| T | period | s |
| f | frequency | Hz |
Rearrangements
f = 1 / T
Worked example
Common trap
Understanding period and frequency
The relationship T = 1 / f connects the period of an oscillation or wave to its frequency. T is the period in seconds (s), the time for one complete cycle, and f is the frequency in hertz (Hz), the number of complete cycles each second.
Period and frequency describe the same repetition from opposite viewpoints, so they are reciprocals of each other. If one complete cycle takes a short time, many cycles fit into each second, so a small period means a large frequency and vice versa.
The formula rearranges simply to f = 1 / T. Because they are reciprocals, T × f = 1.
Keep the period in seconds and the frequency in hertz, converting any milliseconds to seconds first.
A worked example, step by step
A vibrating string produces a wave whose period is T = 0.004 s. Find the frequency.
Apply the reciprocal relationship:
f = 1 / T = 1 / 0.004 s = 250 Hz.
Dividing 1 by a time in seconds gives a value in s⁻¹, which is the hertz, so f = 250 Hz (3 significant figures). As a check, T × f = 0.004 s × 250 Hz = 1, confirming the two are reciprocals.
If the period were halved to 0.002 s, the frequency would double to 500 Hz.
Common mistakes and how this is tested
The classic error is swapping the two quantities, using f where T belongs. Remember the period is a time in seconds and the frequency is a rate in hertz; they are never equal unless both are 1.
Other mistakes: leaving the period in milliseconds (0.004 s, not 4); forgetting to take the reciprocal at the end; and misreading a period off a graph by measuring only half a cycle.
Under calculate show T = 1 / f or f = 1 / T, substitute with the unit and state the answer’s unit. Under define you may be asked to define period and frequency separately.
Under explain, you might describe why a shorter period corresponds to a higher frequency.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)