AQA GCSE Combined Science: Trilogy Physics Paper 2 (Higher), 2022: Question 1

✅ Correct answers

• A = rarefaction
• B = wavelength

💡 Key knowledge

• A rarefaction is the spread-out part of a longitudinal wave.
• A compression is the close-together part.
• Wavelength is the distance between two matching points on a wave, such as from one compression to the next compression, or one rarefaction to the next rarefaction.

🧠 Exam technique

When the diagram shows dots close together and far apart, think:

• close together = compression
• spread out = rarefaction
• horizontal distance across one full pattern = wavelength

❌ Common errors

• Choosing amplitude for B. Amplitude is not shown by this horizontal double arrow.
• Choosing frequency or reflection, which are not labels for parts of this diagram.
• Mixing up compression and rarefaction.

✅ Correct answer

Period = 0.00025 s

📐 Calculation

1. Convert the frequency into hertz:
   4.0 kHz = 4000 Hz
2. Use the equation:
   T = 1 / f
3. Substitute the value:
   T = 1 / 4000
4. Calculate:
   T = 0.00025 s

💡 Key knowledge

• Period means the time for one complete wave.
• Frequency means the number of waves per second.
• Period and frequency are linked by:
  T = 1 / f

🧠 Exam technique

• Always convert kHz to Hz first.
• Write the equation before substituting numbers.
• Give the final unit. A missing unit can cost a mark.
• Even if you get the conversion wrong, correct method can still earn marks.

❌ Common errors

• Using 4.0 instead of 4000 .
• Forgetting that kilo = 1000.
• Writing the answer in Hz instead of seconds.
• Using the wrong equation, such as v = f × λ , which is not needed here.

✅ Correct answer

wave speed = frequency × wavelength

or

v = f × λ

💡 Key knowledge

• v = wave speed in m/s
• f = frequency in Hz
• λ = wavelength in m

🧠 Exam technique

This is a pure recall mark. Learn this equation exactly as it appears on the Physics Equations Sheet.

❌ Common errors

• Writing T = 1 / f instead.
• Missing out one of the symbols.
• Putting the terms in a form that does not mean the same thing.

✅ Correct answer

Wavelength = 1.16 m

📐 Calculation

1. Read the wave speed from Figure 2 at 28.0 °C:
   v = 348 m/s
2. Write the wave equation:
   v = f × λ
3. Substitute values:
   348 = 300 × λ
4. Rearrange:
   λ = 348 / 300
5. Calculate:
   λ = 1.16 m

💡 Key knowledge

• Sound travels faster at higher air temperatures.
• To find wavelength:
  λ = v / f
• Wavelength should be in metres (m).

🧠 Exam technique

• Read the graph carefully before doing any calculation.
• Use a sensible value from the graph. Here, 348 m/s is best.
• Show substitution and rearrangement clearly to collect method marks.
• If your graph reading is slightly off, you can still gain follow-through marks if the method is correct.

❌ Common errors

• Using 330 m/s instead of reading from the graph. The mark scheme says this can score a maximum of 2 marks only.
• Rearranging wrongly, for example doing 300 / 348 .
• Forgetting the unit m .
• Not using the graph value at 28 °C.

💡 What separated stronger answers

• They knew the key vocabulary: rarefaction and wavelength.
• They converted 4.0 kHz to 4000 Hz before calculating period.
• They quoted the correct equation v = f × λ from memory.
• They read the graph carefully and used a realistic speed value close to 348 m/s.
• They included units in both calculations.

❌ Where students lost marks

• Confusing wave features in the longitudinal wave diagram.
• Not converting kilohertz into hertz.
• Giving a number without a unit.
• Using remembered approximate sound speed instead of the graph.
• Not showing enough working to earn method marks.

🧠 Full-mark strategy

1. Identify the physics idea first: wave feature, period equation, or wave equation.
2. Write the equation before the numbers.
3. Convert units if needed.
4. Substitute carefully.
5. Rearrange clearly.
6. Check the final unit matches the quantity asked for.