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Playbook

Sound

34 q · 3% HARD — the bank's lowest-HARD chapter. Properties of sound (amplitude, pitch, loudness), v=fλ plug-in, SONAR, beats, ear anatomy. Pure recall + one-step calc.

questions in the bank
34
tagged HARD
3%
subtopic(s)
4
worked examples
2

When you’ll see it

A sound-property statement, a v=fλ plug-in, a SONAR distance, an ear-anatomy match, or a beats question.

How this chapter is tested

34 q in 10 years, 1 HARD across the whole chapter. NDA's lowest-difficulty chapter. The work is recognition: 'amplitude controls loudness, frequency controls pitch, waveform controls quality' — the three-line table memorised cold answers 60% of the recall items.

v = f·λ is the one formula. Speed of sound in air ≈ 343 m/s at 20 °C, in water ≈ 1500 m/s, in steel ≈ 5000 m/s. SONAR (water echolocation, ships) and ultrasound (medical imaging, bat navigation) use the same echo formula d = v·t/2.

Ear anatomy: ossicles (hammer-anvil-stirrup) transmit, cochlea converts pressure→electrical via hair cells, auditory nerve carries signal to brain. Test rarely goes deeper than 'which part converts to electrical signal' (cochlea/hair cells).

The sub-skills

The rules and habits that decide whether you get a question right.

  • Sound property mapping

    Amplitude → loudness (dB). Frequency → pitch (Hz). Waveform → timbre / quality. NEVER swap them.

  • v = f·λ plug-in

    Identify which of {v, f, λ} is given and which is missing. Convert units (cm → m, Hz → kHz) before plugging.

  • Echo / SONAR formula

    Round trip is 2d. d = v·t/2. For SONAR in water v ≈ 1500 m/s, in air v ≈ 343 m/s. Watch the divide-by-2.

  • Ear → SONAR vocabulary recall

    Audible range 20 Hz – 20 kHz, infrasound < 20 Hz, ultrasound > 20 kHz. Bats use ultrasound; whales use a mix; humans hear neither extreme.

2 worked examples from the bank

Real past-year questions illustrating the playbook. Click to reveal options + solution.

Example 1SoundMODERATE
The speed of sound in a large ideal gas container is xx. When pressure is doubled at constant temperature, speed becomes yy. What is x/yx/y?

[Q62 · Apr · 2026]

Example 2SoundMODERATE
A sound wave has a frequency of 1 kHz and wavelength 50 cm. How long will it take to travel 1 km?

[Q83 · Apr · 2022]

Traps to expect

Distractor shapes specific to this chapter. The page-wide Traps section covers the bank-level patterns.

  • Amplitude in Hz

    Wrong option says 'amplitude is measured in Hz.' Amplitude is pressure or displacement, NOT frequency. Hz belongs to frequency.

  • Forgetting /2 on echo

    d = v·t (whole trip) vs d = v·t/2 (one-way). The trap option uses the whole trip — picks v·t as the distance.

Drill every sound question

34 questions from the bank, scoped to 4 bundled subtopics.

Drill the 34 questions

Related playbooks

Often paired with this one — drill these next if you found the worked examples above tractable.