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Light and Sound - Pitch and Volume

Grade 3IB

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

🔑Concepts

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Sound is produced by vibrations, which are rapid back-and-forth movements of particles.

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Pitch is the quality that allows us to classify a sound as 'high' or 'low'. It depends on the frequency (ff) of the vibration.

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Frequency (ff) is the number of vibrations per second. High frequency (f↑f \uparrow) creates a high pitch, while low frequency (f↓f \downarrow) creates a low pitch.

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Pitch is measured in units called Hertz (HzHz).

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Volume (Loudness) is how loud or soft a sound is. It is determined by the amplitude (AA) of the vibration.

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Amplitude (AA) is the size or strength of the vibration. Larger vibrations (A↑A \uparrow) result in louder sounds, measured in decibels (dBdB).

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Short or thin objects usually vibrate faster, creating a higher pitch, while long or thick objects vibrate slower, creating a lower pitch.

📐Formulae

f=Total vibrationsTime in secondsf = \frac{\text{Total vibrations}}{\text{Time in seconds}}

Pitch∝f\text{Pitch} \propto f

Volume∝Amplitude (A)\text{Volume} \propto \text{Amplitude (A)}

Frequency (Hz)=1T where T is the time period\text{Frequency (Hz)} = \frac{1}{T} \text{ where } T \text{ is the time period}

💡Examples

Problem 1:

A guitar string vibrates 440440 times in one second. If another string vibrates 220220 times in one second, which string has the higher pitch?

Solution:

The string vibrating 440440 times per second has the higher pitch.

Explanation:

Since pitch is directly proportional to frequency (ff), the string with the higher frequency (440Hz>220Hz440 Hz > 220 Hz) produces a higher sound.

Problem 2:

If you strike a drum with a lot of force, the skin moves a distance of 5mm5 mm. If you strike it lightly, it moves 1mm1 mm. How does the volume change?

Solution:

The volume is much louder when the drum is struck with more force.

Explanation:

Striking the drum harder increases the amplitude (AA) of the vibration from 1mm1 mm to 5mm5 mm. Because Volume∝A\text{Volume} \propto A, a larger amplitude creates a louder sound.

Problem 3:

Two tuning forks are used. Fork A has a frequency of 512Hz512 Hz and Fork B has a frequency of 256Hz256 Hz. Which one sounds deeper (lower)?

Solution:

Fork B sounds deeper.

Explanation:

A lower frequency (256Hz256 Hz) results in a lower pitch. In music, a lower pitch is often described as a 'deeper' sound.