Sound Properties (Amplitude, Period, Frequency, Wavelength) | Physics | Khan Academy

Summary

The video explains sound waves, their behavior, and key concepts like amplitude, frequency, period, and wavelength. It shows how sound waves can be visualized using an oscilloscope, with the horizontal axis representing time and the vertical axis representing air molecule displacement. Amplitude determines loudness, while the period and frequency influence pitch. The wavelength represents the distance between compressed air regions. The difference between displacement vs. time and displacement vs. position graphs is highlighted, explaining how they reflect the period and wavelength of sound waves, respectively.

Takeaways

• 🎵 Sound waves can be represented visually using an oscilloscope, which shows their oscillations on a graph.
• 📊 The horizontal axis of a sound wave graph represents time, and the vertical axis represents the displacement of air molecules as they oscillate.
• 🔊 The amplitude of a sound wave refers to the maximum displacement of an air molecule from its equilibrium position, not the entire displacement.
• ⏳ The period of a sound wave is the time it takes for one air molecule to oscillate back and forth once, measured in seconds.
• 🎶 The frequency of a sound wave is the number of oscillations per second, measured in hertz (Hz), with 440 Hz being the frequency of the musical note A.
• 👂 Humans can hear frequencies between 20 Hz and 20,000 Hz, while dogs can hear sounds as high as 40,000 Hz.
• 📏 The wavelength of a sound wave is the distance between two compressed regions of air molecules and is measured in meters.
• ⚠️ The period is often confused with the wavelength; however, the period is the time for one oscillation, while the wavelength is the distance between compressed regions in space.
• 📈 A displacement versus time graph represents how a single air molecule moves as time progresses, where peaks indicate the period of the wave.
• 🗺️ A displacement versus position graph provides a snapshot of all air molecules at a specific moment, where the distance between peaks represents the wavelength of the wave.

Q & A

What does a sound wave look like when visualized?

A sound wave can be visualized as a graph that resembles a sine or cosine curve, showing the displacement of air molecules over time.

How is the amplitude of a sound wave defined?

The amplitude of a sound wave is the maximum displacement of an air molecule from its equilibrium position.

What is the difference between amplitude and the entire displacement of an air molecule?

The amplitude is only the maximum displacement from the equilibrium position, not the length of the entire back-and-forth movement.

What is the period of a sound wave?

The period of a sound wave is the time it takes for an air molecule to fully move back and forth one time, also known as one cycle.

How is the frequency of a sound wave related to its period?

The frequency of a sound wave is the reciprocal of its period, measured in oscillations per second or hertz.

What is the typical range of frequencies for human hearing?

Humans can hear frequencies ranging from about 20 hertz to about 20,000 hertz.

What is the frequency of an A note that causes air to oscillate back and forth 440 times per second?

The frequency of an A note that oscillates 440 times per second is 440 hertz.

What is the relationship between the frequency of a sound and the pitch we perceive?

Higher frequencies correspond to higher pitches, and lower frequencies correspond to lower pitches.

What is the wavelength of a sound wave, and how is it measured?

The wavelength of a sound wave is the distance between two compressed regions of air and is measured in meters.

How does the displacement versus time graph differ from the displacement versus position graph in representing a sound wave?

A displacement versus time graph shows the movement of a single air molecule over time, representing the period. A displacement versus position graph shows a snapshot of all air molecules' displacement at a moment, representing the wavelength.

Why do people often confuse the period and wavelength of a sound wave?

People confuse period and wavelength because they are both represented by the interval between peaks in different types of graphs, but they measure different aspects of the wave.