Required practical 1 - Stationary Waves on a String

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Last updated 11:14 AM on 6/4/26
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11 Terms

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Apparatus and equipment for experiment

  • Signal generator: To create the frequency needed to induce waves on the string.

  • Vibration generator: Connects to the string to produce vibrations.

  • Stand and pulley system: To support the string and apply tension.

  • Wooden bridge: To adjust the length of the vibrating section of the string.

  • 100g masses with holder: To create tension in the string (9.81 N when using 100g).

  • Metre ruler: To measure the vibrating length of the string.

  • 1.5m long string: Used to produce the waves.

  • Balance: To measure the mass of the string for calculating mass per unit length.

<ul><li><p><strong>Signal generator</strong>: To create the frequency needed to induce waves on the string.</p></li><li><p><strong>Vibration generator</strong>: Connects to the string to produce vibrations.</p></li><li><p><strong>Stand</strong> and <strong>pulley</strong> system: To support the string and apply tension.</p></li><li><p><strong>Wooden bridge</strong>: To adjust the length of the vibrating section of the string.</p></li><li><p><strong>100g masses with holder</strong>: To create tension in the string (<span><strong>9.81 N</strong></span> when using 100g).</p></li><li><p><strong>Metre ruler</strong>: To measure the vibrating length of the string.</p></li><li><p><span style="line-height: 27px;">1.5</span><strong>m long string</strong>: Used to produce the waves.</p></li><li><p><strong>Balance</strong>: To measure the mass of the string for calculating mass per unit length.</p></li></ul><p></p>
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Step 1 of experiment

Set up the apparatus as shown in the diagram

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Step 2 of experiment

Adjust the length l so that it is 1.000m, measured using the metre ruler.

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Step 3 of experiment

Adjust Frequency: Increase the frequency using the signal generator until the string vibrates at the first harmonic. This is the lowest frequency at which a stationary wave forms on the string, creating a single loop. Record the frequency f.

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Step 4 of experiment

Reduce l by 0.100m and adjust f again until it oscillates at the first harmonic

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Step 5 of experiment

Repeat the experiment twice more and find and record the mean f for each l.

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Step 6 of experiment

Measure the mass of the string on the balance and record it.

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Graph

  • Plot a graph of the mean value of f against 1/l and draw a line of best fit. The wave speed will be two times the gradient.

  • λ = 2l ⇒ v = 2fl = 2/ 1/l => 2G where G is the gradient.

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Calculations

  • The tension of the string is equal to the weight of the hanging mass (if 100g, 0.981N) and its mass per unit length can be found by dividing the mass of the string by its length (1.5m).

  • The speed of the wave is also given by v = T/√μ which can be compared to the value obtained by the graph.

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Safety

The stand could topple over and cause injury so a counterweight can be used if it is deemed unstable.

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Improvements + notes

  • The experiment can be repeated with different masses to change the tension and different thicknesses of string to change the mass per unit length in order to investigate the effect of changing these parameters.

  • An oscilloscope can be used to verify the signal generator’s readings.

  • The signal generator should be left for about 20 minutes to stabilise.