Core Practical: Measuring waves (Edexcel GCSE Physics Combined Science): Revision Notes
📚 Revision Notes
Core practical: Measuring waves
In real-life applications, understanding how to measure the speed of waves is crucial. The speed of a wave tells us how fast energy is being transferred through a substance. Here, we'll look at how to measure wave speed in air, water, and solids using different techniques.
1. Measuring Sound Waves in Air Using an Oscilloscope
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Method:
- Gather Equipment: You will need two microphones, an oscilloscope, a loudspeaker, and a signal generator.
- Set up the Equipment:
- Attach the loudspeaker to the signal generator and note the frequency.
- Connect the microphones to the oscilloscope to see the sound wave trace.
- Separate the Microphones: Move the microphones so that their signals appear as two separate waves on the oscilloscope.
- Align the Wavelengths: Slowly move one microphone away until the waves on the oscilloscope are aligned exactly one wavelength apart.
- Measure the Distance: The distance between the microphones is the wavelength of the sound wave.
- Calculate Wave Speed: Use the wave speed formula:
- Frequency comes from the signal generator.
- Wavelength is the distance measured between the microphones.
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2. Measuring Water Waves Using a Strobe Light and Ripple Tank
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Method:
- Set Up the Ripple Tank: Attach a signal generator to a dipper in the ripple tank to create water waves at a set frequency.
- Use a Strobe Light: Dim the lights and use a strobe light to observe the wave pattern created by the shadows of wave crests.
- Freeze the Pattern: Adjust the strobe light's frequency until the wave pattern freezes, meaning the strobe light matches the frequency of the water waves.
- Measure the Wavelength: Measure the distance between shadow lines that represent wave crests, then divide by the number of wavelengths to find the average wavelength.
- Calculate Wave Speed: Use the wave speed formula:
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3. Measuring Waves in Solids Using Peak Frequency
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Method:
- Measure the Rod: Record the length of the solid rod you are testing.
- Set Up the Apparatus: Secure the rod at its centre and connect it to equipment to measure frequency.
- Tap the Rod: Strike the rod with a hammer and measure the peak frequency of the sound waves produced.
- Repeat and Average: Perform the experiment three times and calculate the average frequency.
- Calculate Wave Speed: Use the formula:
- The wavelength is twice the length of the rod.
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Calculating Wave Speed: Key Formula
For all types of waves, the formula for wave speed is:
- Wave speed: Measured in metres per second (m/s).
- Frequency: Measured in hertz (Hz).
- Wavelength: Measured in metres (m).
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Example Calculation:
Question: What is the speed of a wave with a frequency of 100 Hz and a wavelength of 2 m?
- Write out the equation:
- Substitute the values:
So, the wave speed is 200 m/s.