Waves - Properties of Sound

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Sound is a longitudinal mechanical wave that requires a medium (solid, liquid, or gas) to travel; it cannot travel through a vacuum.

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Sound travels through a series of compressions (high pressure) and rarefactions (low pressure) in the medium.

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f

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A

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20\text{ Hz}

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v

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Echoes are the reflection of sound waves off a surface. For a clear echo, the reflecting surface must be at a sufficient distance to distinguish the original sound from the reflected one.

📐Formulae

v = f \lambda

f = \frac{1}{T}

v = \frac{2d}{t} \text{ (for echoes/reflection)}

\text{Speed} = \frac{\text{Distance}}{\text{Time}}

💡Examples

Problem 1:

440\text{ Hz}

Solution:

\lambda = \frac{v}{f} = \frac{340\text{ m/s}}{440\text{ Hz}} \approx 0.77\text{ m}

Explanation:

v = f\lambda

Problem 2:

1.2\text{ seconds}

Solution:

d = \frac{v \times t}{2} = \frac{1500\text{ m/s} \times 1.2\text{ s}}{2} = 900\text{ m}

Explanation:

2d

Problem 3:

T

Solution:

T = \frac{1}{f} = \frac{1}{2000\text{ Hz}} = 0.0005\text{ s} = 0.5\text{ ms}

Explanation:

2\text{ kHz}