AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2021: Question 3

11 marks · Standard Demand difficulty · Extended Answer

Describe how to measure the frequency and wavelength of water waves in a ripple tank, calculate the mean wave speed from repeated readings, explain the benefit of repeats, and relate water depth to wavelength at constant frequency.

Practise this question

Question

The question page shows a physics ripple tank problem split into four parts labelled 03.1 to 03.4. Part 03.1 asks the student to describe how the frequency and wavelength of water waves in a ripple tank can be measured accurately for 4 marks, with lined space for an extended written response. Below, two small tables give three readings of frequency in hertz as 9.8, 9.4 and 9.3, and wavelength in centimetres as 1.7, 2.2 and 2.1; part 03.2 asks for the mean wave speed for 4 marks, part 03.3 asks the advantage of repeat readings and calculating a mean for 1 mark, and part 03.4 states that deeper water makes waves faster and asks how depth affects wavelength if frequency is constant for 2 marks.
Question text

03 A student made water waves in a ripple tank.

03.1 Describe how the frequency and wavelength of the water waves in the ripple tank can

be measured accurately.

[4 marks]

The student recorded values for the frequency and the wavelength of waves in the

ripple tank.

Table 1 and Table 2 show the results.

Table 1

Reading 1 2 3

Frequency

9.8 9.4 9.3

in hertz

Table 2

Reading 1 2 3

Wavelength

1.7 2.2 2.1

in cm 11

03.2 Determine the mean wave speed.

[4 marks]

Mean wave speed = m/s

03.3 What is the advantage of taking repeat readings and then calculating a mean?

[1 mark]

03.4 The speed of the wave is affected by the depth of the water in the ripple tank.

The deeper the water the faster the wave.

Explain how the depth of the water affects the wavelength of the wave if the frequency

is constant.

[2 marks]

Mark scheme

Show the mark scheme The mark scheme is a table listing answers for questions 03.1 to 03.4. For 03.1, a level-of-response scheme awards up to 4 marks for a valid, logically sequenced method describing both wavelength and frequency measurements, including ideas such as using a metre rule perpendicular to wave fronts, measuring across several waves or the screen image, photographing the pattern, timing waves past a point with a stopwatch, or using video and counting waves in one second. For 03.2, the scheme gives mean frequency 9.5 hertz, mean wavelength 0.020 metres, and wave speed 0.19 metres per second, with credit for correct substitution or averaging individual speed values; 03.3 awards 1 mark for reducing random error or allowing anomalous readings to be discarded, and 03.4 awards 2 marks for saying deeper water gives a longer wavelength because wave speed increases while frequency stays constant.

AO /

Question Answers Mark

Spec. Ref.

03.1 Level 2: The design/plan would lead to the production of a valid 3–4 AO1

outcome. All key steps are identified and logically sequenced. 6.6.1.2

Level 1: The design/plan would not necessarily lead to a valid 1–2

outcome. Most steps are identified, but the plan is not fully logically

sequenced.

No relevant content 0

Indicative content

Wavelength

• place a metre rule at the side of the screen perpendicular to the

wave fronts

• use the metre rule to measure the length of the screen

• take a photograph of the shadow on the screen

• count the number of complete waves on the screen

• determine the wavelength by dividing the length of the by the

number of complete waves

or

• place a metre rule at the side of the screen perpendicular to the

wave fronts

• take a photograph of the shadow on the screen

• use the metre rule to measure the distance between two wave

front

Frequency

• count the number of waves that pass a given point

• time how long it takes for the waves to pass that point using a

stop clock

• frequency is number of waves divided by time taken

or

• put a stop clock on the screen

• use a digital video camera to record the waves passing a point

• replay in slow motion and count the number of waves passing a

point in 1 second

There must be a description of both frequency and wavelength

measurement to access level 2

03.2 mean f = 9.5 Hz 1 AO2 9

6.6.1.2

mean λ = 0.020 m 1

v = 9.5 × 0.020 allow a correct substitution of an 1

incorrect value of mean

frequency and/or

wavelength

v = 0.19 (m/s) allow a correct calculation using 1

an incorrect value of mean

frequency and/or

wavelength

or

v = 9.8 × 0.017

and

v = 9.4 × 0.022

and

v = 9.3 × 0.021 (2)

(1.67 + 2.07 + 1.95)

v = (1)

v = 0.19 (m/s) (1) allow a maximum of 2 marks if a

single pair of values is used

03.3 reduces the effect of random allow anomalous readings can 1 AO1

errors be discarded before calculating 6.6.1.2

a mean

03.4 deeper water means longer 1 AO3

wavelength 6.6.1.2

because

v increases and f is constant allow for a fixed frequency 1

period is constant

Total 11

How to answer it

Ripple Tank Waves: Measuring, Calculating and Explaining Results

What this question tests
You need to describe a method for measuring wavelength and frequency accurately, use mean values to calculate wave speed with v = f × λ , and explain how repeat readings improve reliability. You also need to apply the idea that if frequency stays constant, a faster wave in deeper water has a longer wavelength.

Question overview

Exam focus: wave measurements in a ripple tank

Key skills

  • Describing a practical method clearly and in order
  • Using repeat readings and calculating a mean
  • Substituting into the wave speed equation
  • Explaining the link between speed, frequency and wavelength

How marks are awarded

  • Marks are for clear method steps, not just naming equipment
  • For calculations, you need the correct mean, correct units and working
  • For explanation questions, one mark is often for the result and one for the reason

Part 03.1 — Describe how the frequency and wavelength can be measured accurately

4 marks — this is a method question. You must describe both wavelength and frequency measurement to reach the top level.

✅ Correct answer

Wavelength:

  • Place a metre rule beside the screen, perpendicular to the wave fronts.
  • Take a photograph or view the pattern on the screen.
  • Measure the distance across several complete waves, or measure the distance between two wave fronts.
  • If measuring several waves, divide the total distance by the number of waves to find the wavelength.

Frequency:

  • Choose a fixed point.
  • Count how many waves pass that point in a measured time using a stop clock.
  • Calculate frequency using frequency = number of waves ÷ time .

💡 Key knowledge

  • Wavelength is the distance between two matching points on adjacent waves, for example crest to crest.
  • Frequency is the number of waves passing a point each second.
  • Accuracy improves by measuring more than one wave and then dividing.
  • A photo helps because the wave pattern can be measured more carefully and checked.

🧠 Exam technique

  • Write the method in a logical order: set up → measure → calculate.
  • Use scientific language such as wave fronts, fixed point and time taken.
  • To gain full marks, do not only say “measure the waves” — explain how.

❌ Common errors

  • Only describing wavelength or only describing frequency — the mark scheme requires both.
  • Saying “use a ruler” without saying where or how to measure.
  • Measuring from one crest to the next over just one wave can be less accurate than using several waves.
  • Not stating that frequency is found from waves per second.

📐 Example of a full-mark method

  1. Place a metre rule along the screen so it is perpendicular to the wave fronts.
  2. Take a photograph of the wave pattern.
  3. Measure the distance across several complete waves.
  4. Count the number of waves in that distance.
  5. Work out wavelength by dividing distance by number of waves.
  6. For frequency, count how many waves pass a fixed point in a measured time.
  7. Calculate frequency using waves ÷ time.

Part 03.2 — Determine the mean wave speed

4 marks — you need to use the mean frequency and mean wavelength, convert units, and apply v = f × λ .

✅ Correct answer

Mean frequency = 9.5 Hz

Mean wavelength = 2.0 cm = 0.020 m

Wave speed = 9.5 × 0.020 = 0.19 m/s

📐 Step-by-step calculation

  1. Find the mean frequency
    (9.8 + 9.4 + 9.3) ÷ 3 = 28.5 ÷ 3 = 9.5 Hz
  2. Find the mean wavelength
    (1.7 + 2.2 + 2.1) ÷ 3 = 6.0 ÷ 3 = 2.0 cm
  3. Convert cm to m
    2.0 cm = 0.020 m
  4. Use the equation
    v = f × λ
    v = 9.5 × 0.020 = 0.19 m/s

💡 Key knowledge

  • The wave speed equation is v = f × λ .
  • Frequency must be in hertz (Hz).
  • Wavelength must be in metres (m) when calculating speed in m/s.
  • Using a mean reduces the effect of random variation in the results.

❌ Common errors and traps

  • Forgetting to convert cm to m.
  • Using the wrong equation or dividing instead of multiplying.
  • Using just one reading instead of the mean when the question asks for the mean wave speed.
  • Giving the answer without units, or with the wrong units.
  • Rounding too early before the final calculation.

🧠 Examiner insight

  • Top answers showed the full working: mean frequency, mean wavelength, unit conversion, then substitution.
  • Students lost marks when they used only one pair of values.
  • The mark scheme allowed some credit even if one mean was wrong, as long as the calculation method was correct.
  • To secure the final mark, the answer had to be sensibly rounded to 0.19 m/s.

Part 03.3 — What is the advantage of taking repeat readings and calculating a mean?

1 mark — this is a short recall-style explanation.

✅ Correct answer

It reduces the effect of random errors.

You may also say that anomalous readings can be identified and ignored before finding the mean.

💡 Key knowledge

  • Repeating measurements makes results more reliable.
  • The mean is usually closer to the true value than a single reading.

❌ Common errors

  • Saying “it makes it more accurate” is less precise than the mark scheme wording.
  • Confusing random errors with systematic errors.
  • Only saying “to get a better answer” without explaining why.

Part 03.4 — Explain how depth affects wavelength if frequency is constant

2 marks — one mark for the trend, one mark for the reason.

✅ Correct answer

As the water gets deeper, the wavelength gets longer.

This is because the wave speed increases in deeper water, and if the frequency stays constant, then v = f × λ means wavelength must increase.

💡 Key knowledge

  • Deeper water → faster wave
  • If frequency is fixed, wavelength changes when speed changes
  • From v = f × λ , if f stays the same and v increases, then λ increases

🧠 Exam technique

  • Use a clear cause-and-effect sentence.
  • Always link the idea back to the equation if you can.
  • For 2 marks, don’t just say “longer wavelength” — explain why.

❌ Common errors

  • Saying deeper water means shorter wavelength — this is the opposite of the mark scheme.
  • Claiming frequency changes when the question says it is constant.
  • Talking only about speed and not wavelength.

Quick revision checklist

Must-remember facts

  • v = f × λ
  • Frequency is measured in Hz
  • Wavelength is measured in m when calculating wave speed
  • Repeat readings reduce random errors

Full-mark habits

  • Describe both frequency and wavelength methods
  • Show means clearly
  • Convert units before the final calculation
  • Finish with the correct unit: m/s

Topics

Physics · P6: Waves

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Physics Paper 2 (Higher), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.