Core Practical 7: Using an Oscilloscope
Aim of the Experiment
- The aim of this experiment is to investigate the frequency of a sound wave using an oscilloscope
- Independent variable = Tuning forks of different frequencies
- Dependent variable = Time period
Equipment List
Method
Measuring the frequency of a sound wave using an oscilloscope
- Connect the microphone to the oscilloscope as shown in the image above
- Test the microphone displays a signal by humming
- Adjust the time base of the oscilloscope until the signal fits on the screen - ensure that multiple complete waves can be seen
- Strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
- Hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
- Freeze the image on the oscilloscope screen, or take a picture of it
- Measure and record the time period of the wave signal on the screen by counting the number of divisions for one complete wave cycle
- Repeat steps 4-6 for a variety of tuning forks
- A possible results table might look like this:
Analysis of Results
- To convert the time period of the wave from the number of divisions into seconds, use the scale of the time base. For example:
- The time base is usually measured in units of ms/cm (milliseconds per centimetre)
- This would mean a wave with a time base of 4 cm has a time period of 4 ms
- To calculate the frequency of the sound waves produced by the tuning forks, use the equation:
- Where:
- f = Frequency, measured in hertz (Hz)
- T = Time period, measured in seconds (s)
Evaluating the Experiment
Systematic Errors:
- Ensure the scale of the time base is accounted for correctly
- The scale is likely to be small (e.g. milliseconds) so ensure this is taken into account when calculating the time period
Random Errors:
- A cause of random error in this experiment is noise in the environment, so ensure it is carried out in a quiet location