IGCSE Physics / Properties of waves
Frequency and time period revision notes
Edexcel International GCSE Physics (4PH1), chapter 10: Properties of waves, specification point 3.6. Free lesson.
Watch the video lesson · IGCSE Physics past papers
Frequency is the number of waves each second, while the time period is the time taken for one wave. They are linked by f = 1/T, which also helps you find wavelength when you combine it with the wave equation.
How frequency and time period are linked
Frequency and time period describe the same repeating wave in different ways. A high frequency means each wave takes a short time, so the time period is small. The equation f = 1/T is on the equation list. You must use T in seconds. Frequency, f, is the number of waves each second, measured in hertz (Hz). Time period, T, is the time for one complete wave, measured in seconds (s). Convert milliseconds to seconds by dividing by 1000: 1 ms = 0.001 s.
How to calculate a time period
Substitute the frequency into f = 1/T, then rearrange to find T. For a frequency of 50 Hz, each wave takes one fiftieth of a second.
How to read a period from an oscilloscope trace
A microphone can turn a sound into a trace on an oscilloscope. Find one complete wave and count how many horizontal squares it covers. Multiply this by the time-base, which gives the time represented by each square. The trace is a steady note. Its amplitude is 2 squares, and with a Y-gain of 1 V per square, the amplitude is 2 V. For the trace shown, one wave covers 4 squares. The time-base is 1 ms per square, so the period is 4 × 1 ms = 4 ms. Convert before using f = 1/T: 4 ms = 0.004 s, so f = 1/0.004 = 250 Hz.
How to find wavelength using frequency
The wave equation is v = f × λ, where v is wave speed in metres per second (m/s), f is frequency in hertz (Hz), and λ is wavelength in metres (m). If you are given the period instead of frequency, find f first using f = 1/T.