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12. Another investigation of waves using a tensioned wire and signal generator

The signal generator produces transverse vibrations in a wire.

A The set-up

This method involves using a signal generator is connected to a vibration transducer.

A longish piece of wire or string is fixed to the vibration transducer and passed over a pulley wheel at the end of the bench.

The other end of the wire/string is connected to a hook system on which you can add 'weights' to increase the tension on the wire/string.

 

B The procedure

You switch on the signal generator and vibration transducer to set the wire/string vibrating - the waves should oscillate up and down.

Adjust the frequency until you can get a clear transverse standing wave (as in diagram B) and measure its wavelength using the metre rule sighted behind the vibrating wire/string.

Its easiest to measure the length of as many half wavelengths as you can, calculate the average and then double the average to get the full wavelength.

You can vary two things:

(i) Vary the weights added to tension the string and measure the wavelength each time for a fixed length of wire/string between the transducer and the pulley wheel.

(ii) Vary the length of the wire/string between the transducer and the pulley wheel for a fixed tension weight.

Obviously, you can do several sets of results within the experimental framework of (i) and (ii).

 

Measurements and calculations

For each set of experiments you should record

the frequency of the standing wave (f in Hz)

the tension on the string/wire (T in N)

the total length of the wire/string (L in m)

the wavelength (λ in m)

and you can calculate the speed too (v = f x λ in m/s).

This gives you loads of data to play with!

You should find that the wavelength of the string wire measured varies with:

(i) The in tension on the wire/string for a fixed length.

You should find the frequency increases and wavelength decreases the greater the tension on the wire/string.

The frequency is proportional to the square root of the tension (f 1/√T).

Think of tightening the tension on a guitar or violin string (fixed length) - the pitch increases the more you tighten it up.

(ii) The length of the wire/string for a fixed tension weight.

You should find that the frequency increases and wavelength decreases the shorter the wire/string.

For a fixed tension weight, the frequency of a stretched string is inversely proportional to the length of the string (f 1/L).

 

Having measured the wavelength (convert to m), and knowing the frequency (Hz) from the generator, you can then calculate the speed of the wave in each case.

speed = frequency x wavelength = v = f x λ = ? m/s

For more see measuring the speed of sound in air

 

INDEX notes: Investigating and introducing the properties of waves

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Key points Introduction to waves: Tensioned wire-signal generator investigation

Information sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks & syllabus-specifications for students taking the UK AQA, Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and CIE GCSE physics 9-1 level science examinations

A structured set of summary revision notes on the tensioned wire–signal generator investigation of waves, aligned with the core requirements across major UK GCSE/IGCSE exam boards (WJEC, CCEA, CIE, AQA, Edexcel, OCR). This practical helps students explore how wave speed depends on tension and frequency - ideal for understanding wave behaviour in strings and solids.

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Tensioned Wire–Signal Generator Investigation

Purpose

To investigate how wave speed in a stretched wire depends on:

• Tension in the wire
• Frequency of the signal
• Length and mass per unit length of the wire

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Apparatus for the tensioned wire-signal generator investigation

• Signal generator
• Tensioned wire (e.g. steel or copper)
• Pulley and hanging mass (to vary tension)
• Vibration transducer or electromagnetic driver
• Meter ruler or measuring tape
• Power supply and clamps

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Method Overview for the tensioned wire-signal generator investigation

1. Connect the wire to a signal generator and stretch it horizontally.
2. Adjust tension using hanging masses.
3. Vary frequency until standing waves (resonance) are observed.
4. Measure the wavelength using the distance between nodes.
5. Use the wave equation to calculate wave speed: [ v = f \times \lambda ]

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Observations from the tensioned wire-signal generator investigation

• Standing waves form at specific frequencies (harmonics).
• Increasing tension increases wave speed.
• Higher frequency = shorter wavelength for same wave speed.

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Variables for the tensioned wire-signal generator investigation

Variable Type	Examples
Independent	Tension (mass), frequency
Dependent	Wavelength, wave speed
Control	Wire length, wire type, temperature

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 Typical Exam Board Coverage of the tensioned wire-signal generator investigation

Wave Speed Equation	Standing Waves	Required Practical
( v = f \lambda )	Harmonics	Wave on string
Wave speed	Resonance	Tensioned wire
Frequency & tension	Nodes/antinodes	Wave investigation
Wave properties	Standing waves	Vibrating string
Wave speed	Harmonics	Signal generator
Wave equation	Resonance	Vibrating wire

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 Student Tips for the tensioned wire-signal generator investigation

• Use a sharp pencil to mark nodes and measure wavelength accurately.
• Practise rearranging the wave equation to solve for different variables.
• Understand how tension affects wave speed - link to musical instruments.
• Record multiple trials and average results for reliability.
• Sketch wave patterns to visualise harmonics and resonance.

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 Common Misconceptions related to the tensioned wire-signal generator investigation

•  “Frequency and wave speed are the same.”
   Frequency affects wave speed only if tension or medium changes.
•  “All frequencies produce standing waves.”
   Only resonant frequencies produce clear standing wave patterns.
•  “Wave speed depends on amplitude.”
   Wave speed depends on tension and medium, not amplitude.
•  “Nodes are points of maximum vibration.”
   Nodes are points of no vibration; antinodes are maximum.

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Keywords, phrases and learning objectives relating to the tensioned wire-signal generator investigation

Be able to interpret an investigation into waves using a tensioned wire connected a signal generator that can be tuned to produce a standing wave.

Know that the signal generator creates transverse waves which can be varied by changing the tension weight or the length of the wire.

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WHAT NEXT?

TOP of page

INDEX physics notes: Introducing the properties of waves

INDEX of all notes on waves, radiation, astronomy etc.

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INDEX notes: Investigating and introducing the properties of waves