Required practical - Waves in fluids Revision Notes for AQA GCSE Physics

Required practical - Waves in fluids

What is this practical about?

This practical helps you learn how to measure the speed, frequency and wavelength of water waves using a ripple tank. You'll discover how these wave properties are connected to each other.

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Understanding the relationships between wave properties is fundamental to physics. This practical gives you hands-on experience with real wave measurements that you can apply to many other wave phenomena.

Aim of the investigation

The goal is to find out if a ripple tank setup can accurately measure wave properties in water. You'll test how well the equipment works for measuring different wave characteristics.

Equipment you need

Ripple tank (shallow water tray)
Motor (creates the waves)
Wave generator (makes regular wave patterns)
Stroboscope (flashing light that "freezes" the waves)
Ruler (for measuring)
A3 paper and pencil (for recording measurements)

Safety first!

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Critical Safety Warning: This practical uses water and electricity together, which can be dangerous. Always follow safety rules and ask your teacher before starting. Ensure all electrical equipment is properly protected and your hands are dry when handling any electrical components.

Method - step by step

Step 1: Set up the equipment

Set up your ripple tank as shown by your teacher. Make sure the water depth is the same everywhere.

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Consistent water depth is crucial because wave speed depends on water depth. Even small variations can affect your measurements significantly.

Step 2: Count the wave frequency

Count how many waves pass a fixed point in one minute. Then divide this number by 60 to get the frequency in hertz (Hz).

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Worked Example: Calculating Frequency

Step 1: Count the waves You count 120 waves passing a point in 1 minute

Step 2: Convert to hertz Frequency = Number of waves ÷ Time in seconds Frequency = 120 ÷ 60 = 2 Hz

Step 3: Measure the wavelength

Use the stroboscope to "freeze" the water waves so you can see them clearly. Measure the distance between several wave crests with a ruler. Divide this distance by the number of waves to get an accurate wavelength measurement.

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Worked Example: Measuring Wavelength

Step 1: Measure across multiple waves You measure 5 wave crests spanning 25 cm

Step 2: Calculate average wavelength Wavelength = Total distance ÷ Number of wavelengths Wavelength = 25 cm ÷ 4 = 6.25 cm (Note: 5 crests = 4 complete wavelengths)

Step 4: Calculate wave speed

Use the wave equation:

$\text{Wave speed} = \text{frequency} \times \text{wavelength}$

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Worked Example: Calculating Wave Speed

Using our previous examples:

Frequency = 2 Hz
Wavelength = 6.25 cm = 0.0625 m

Wave speed = 2 × 0.0625 = 0.125 m/s

Key physics concept

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Fundamental Wave Relationship

In water of constant depth, wave speed stays the same no matter what frequency you use. This means:

If frequency increases, wavelength decreases
If frequency decreases, wavelength increases
The wave speed remains constant

This inverse relationship maintains the wave equation: $v = f\lambda$

Getting accurate results

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Measurement Tips for Accuracy

To measure wavelength accurately:

Measure across several waves, not just one
Divide the total distance by the number of waves
This reduces measurement errors and gives you a better average
Always measure from crest to crest or trough to trough for consistency

What the results show

Your results table should show that even when frequency and wavelength change, the wave speed stays roughly the same. This proves the wave equation works for water waves and demonstrates the inverse relationship between frequency and wavelength.

How to improve this investigation

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Enhancement Strategies

Use smaller wavelengths and frequencies for more accurate results
Take multiple measurements and calculate averages
Make sure water depth is exactly the same everywhere
Check the stroboscope is working properly to "freeze" waves clearly
Use a timer for more accurate frequency measurements
Consider the effect of wave reflexion from tank edges

Remember!

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Key Points to Remember:

Wave equation: $v = f\lambda$ (Wave speed = frequency × wavelength)
Water wave speed stays constant in water of the same depth
Measure across multiple waves to reduce errors
Safety is essential when mixing water and electricity
A ripple tank is a suitable method for measuring wave properties in fluids
Frequency and wavelength have an inverse relationship when wave speed is constant

Required practical - Waves in fluids (AQA GCSE Physics): Revision Notes