Edexcel IGCSE Physics 复习笔记 3.3.3 Core Practical: Using an Oscilloscope

Aim of the Experiment

• The aim of this experiment is to investigate the frequency of a sound wave using an oscilloscope

Variables

• Independent variable = Tuning forks of different frequencies
• Dependent variable = Time period

Equipment List

Method

Measuring the frequency of a sound wave using an oscilloscope

1. Connect the microphone to the oscilloscope as shown in the image above
2. Test the microphone displays a signal by humming
3. Adjust the time base of the oscilloscope until the signal fits on the screen - ensure that multiple complete waves can be seen
4. Strike the tuning fork on the edge of a hard surface to generate sound waves of a pure frequency
5. Hold the tuning fork near to the microphone and observe the sound wave on the oscilloscope screen
6. Freeze the image on the oscilloscope screen, or take a picture of it
7. Measure and record the time period of the wave signal on the screen by counting the number of divisions for one complete wave cycle
8. 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

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