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Light and Sound - Vibrations and Sound Production

Grade 3IB

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

🔑Concepts

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Sound is a form of energy produced by vibrations. A vibration is a rapid back-and-forth movement of an object.

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Pitch refers to how high or low a sound is. It is determined by the frequency (ff) of the vibration. High-frequency vibrations produce high-pitched sounds, while low-frequency vibrations produce low-pitched sounds.

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Volume (loudness) is determined by the strength or amplitude of the vibration. Larger vibrations move more air and create louder sounds.

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Sound requires a medium to travel. It can travel through solids, liquids, and gases. It cannot travel through a vacuum because there are no particles to carry the vibration.

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The speed of sound varies depending on the medium. Generally, sound travels fastest through solids because the particles are packed tightly together: vsolid>vliquid>vgasv_{solid} > v_{liquid} > v_{gas}.

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When an object vibrates, it causes the particles in the air (O2O_2, N2N_2, etc.) to bump into each other, creating a sound wave.

📐Formulae

Frequency (f)=Number of VibrationsTime (s)\text{Frequency (} f \text{)} = \frac{\text{Number of Vibrations}}{\text{Time (s)}}

v=f×λv = f \times \lambda

Loudness∝Amplitude\text{Loudness} \propto \text{Amplitude}

💡Examples

Problem 1:

If a guitar string vibrates 440440 times in one second, what is the frequency of the sound produced?

Solution:

f=440 Hzf = 440 \text{ Hz}

Explanation:

Frequency is measured in Hertz (Hz\text{Hz}), which represents the number of vibrations per second. Since the string vibrates 440440 times in 11 second, the frequency is 440 Hz440 \text{ Hz}.

Problem 2:

Why does a short plastic ruler produce a higher pitch than a long plastic ruler when flicked against a desk?

Solution:

The shorter ruler has a higher frequency (ff) of vibration.

Explanation:

Short objects have less mass to move and can vibrate back and forth much faster than long objects. Faster vibrations result in a higher pitch.

Problem 3:

Rank the speed of sound (vv) through a wooden table, a swimming pool, and the air from slowest to fastest.

Solution:

vair<vwater<vwoodv_{air} < v_{water} < v_{wood}

Explanation:

Sound travels slowest in gases like air, faster in liquids like water, and fastest in solids like wood because the particles in solids are closer together, allowing the vibration to pass along more quickly.