OCR · A-Level · Physics
Course version: H556 · Version from Sept 2015
(ii) techniques and procedures used to use an oscilloscope to determine…
Full specification wording
Wave motion: (ii) techniques and procedures used to use an oscilloscope to determine frequency
An oscilloscope displays a signal as a trace on a screen with a calibrated grid.
Checked against the OCR H556 specification (opens in a new tab) on .
- Point 3 of 11
Study notes
From the checked teaching notes for this specification point.
The idea
An oscilloscope displays a signal as a trace on a screen with a calibrated grid. To determine frequency, connect the signal to the input and adjust the time-base control, which sets the time represented by each horizontal division. Read the horizontal distance for one complete cycle, the period T, by counting divisions between successive identical points such as crest to crest, then multiply by the time-base setting to convert divisions into seconds. Frequency is then f = 1/T. For example, if one cycle spans 4.0 divisions and the time-base is 5.0 ms per division, then T = 4.0 × 5.0 ms = 20 ms = 0.020 s, so f = 1/0.020 = 50 Hz. Adjust the vertical gain only to make the trace a convenient size; it does not affect the period measurement.
What earns the marks
- Connect the signal to the oscilloscope input and obtain a steady trace.
- Adjust the time-base so that several complete cycles are visible and the period can be measured accurately.
- Read the number of horizontal divisions for one complete cycle and multiply by the time-base setting to find the period T.
- Convert the period to seconds before calculating frequency.
- Calculate frequency using f = 1/T.
- Recognise that the vertical gain control affects the displayed amplitude, not the measured period.
Common mistakes and how to put them right
Reading the peak-to-peak height as the period.
Put it right: The period is a horizontal distance; the vertical scale gives amplitude, not time.
Forgetting to multiply the number of divisions by the time-base setting.
Put it right: Divisions alone are not a time; convert using the time-base value.
Leaving the period in milliseconds when calculating frequency.
Put it right: Convert to seconds first, so that f = 1/T gives hertz.
Changing the vertical gain and expecting the period to change.
Put it right: Vertical gain alters the trace height only; the time-base controls the horizontal scale.
Exam tips
- Count divisions across several cycles and divide to reduce the uncertainty in one period.
- Write the time-base setting with its unit and convert to seconds before using f = 1/T.
- State clearly which control sets the time scale and which sets the vertical scale.
Try the lesson
The start of the Wave motion: (ii) techniques and procedures used to use an oscilloscope to determine frequency lesson, made from checked teaching notes for this specification point.
Listen
An oscilloscope displays a signal as a trace on a screen with a calibrated grid. To determine frequency, connect the signal to the input and adjust the time-base control, which sets the time represented by each horizontal division. Read the horizontal distance for one complete cycle, the period T, by counting divisions between successive identical points such as crest to crest, then multiply by the time-base setting to convert divisions into seconds. Frequency is then f = 1/T. For example, if one cycle spans 4.0 divisions and the time-base is 5.0 ms per division, then T = 4.0 × 5.0 ms = 20 ms = 0.020 s, so f = 1/0.020 = 50 Hz. Adjust the vertical gain only to make the trace a convenient size; it does not affect the period measurement. A strong answer earns marks for these points. Connect the signal to the oscilloscope input and obtain a steady trace. Adjust the time-base so that several complete cycles are visible and the period can be measured accurately. Read the number of horizontal divisions for one complete cycle and multiply by the time-base setting to find the period T. Convert the period to seconds before calculating frequency. A common slip: Reading the peak-to-peak height as the period. Instead, the period is a horizontal distance; the vertical scale gives amplitude, not time. Exam tip: Count divisions across several cycles and divide to reduce the uncertainty in one period.
See it
Label the diagram
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