Section 1 of 5What the Oscilloscope Shows
What the Oscilloscope Shows
Purpose
- An oscilloscope displays a rapidly changing signal, such as a sound wave or an alternating current, as a trace on a screen.
Microphone
- A microphone changes the sound into an electrical signal, which the oscilloscope plots against time.
Transverse appearance
- Sound is a longitudinal wave, but the trace is drawn as a wave shape that looks like a transverse wave.
Axes
- The horizontal axis shows time, set by the time base, and the vertical axis shows the voltage of the signal.
Section 2 of 5Reading the Trace
Amplitude
- The height of the wave above the centre line is the amplitude, which relates to how loud the sound is.
Period
- The time for one complete wave is found by counting divisions across one cycle and multiplying by the time base setting.
Frequency
- Frequency is the number of waves per second, found from f = 1 ÷ T, where T is the time period in seconds.
More waves
- If the frequency increases, more complete waves fit on the screen when the time base stays the same.
Controls
- Changing the time base stretches or squashes the wave horizontally, and changing the gain alters its height.
Section 3 of 5Worked Reading
1
Count the horizontal divisions occupied by one full wave cycle on the screen.
2
Multiply the number of divisions by the time base, for example 2 ms per division.
3
Convert the result to seconds to find the period T.
4
Calculate the frequency using f = 1 ÷ T.
5
Measure the peak height in divisions and multiply by the volts per division to find the signal amplitude.
| Control | Changes | Effect on display |
|---|---|---|
| Time base | Seconds per division | Wave stretched or squashed horizontally |
| Gain | Volts per division | Wave taller or shorter |
| Louder sound | Amplitude increases | Taller trace |
| Higher pitch | Frequency increases | More waves on screen |
Section 4 of 5Worked Example
Question
- On an oscilloscope with a time base of 2.0 ms per division, one complete wave cycle spans 2.5 divisions.
- Calculate the period and frequency of the sound.
- Period T = 2.5 × 2.0 ms = 5.0 ms.
- Convert5.0 ms = 0.0050 s.
- Frequency f = 1 ÷ T = 1 ÷ 0.0050 = 200 Hz.
Answer Period 5.0 ms and frequency 200 Hz.
Section 5 of 5Exam Checklist & Tips
1.3.2 – Key Points for the Exam
- Oscilloscope A device that displays how a signal varies with time.
- Time base The setting that sets the time represented by each horizontal division.
- Amplitude The maximum displacement of a wave from its rest position.
- Time period The time taken for one complete wave to pass, measured in seconds.
- Frequency The number of complete waves per second, measured in hertz (Hz).
Common Mistakes
- Reading the horizontal axis as distance when it shows time.
- Forgetting to convert milliseconds to seconds before using f = 1 ÷ T.
- Measuring the full height from peak to trough and calling it the amplitude.
- Confusing a change in the time base with a change in the sound itself.