Understanding Sound as a Wave Disturbance Sound Definition: Sounds are wave disturbances that travel by pushing and pulling air molecules. Generation of Sound: When a person shouts, their vocal chords vibrate periodically, causing the air between their mouth and the listener's ear to carry these sound waves. Perception of Sound: These air vibrations strike the listener's eardrums, causing them to vibrate, which the brain then interprets as sound. Frequency and Pitch: Every sound is characterized by a number—its frequency—which measures how fast the source (e.g., vocal cords) vibrates (to-and-fro oscillations per second). The unit of frequency is Hertz (Hz): $1 \text{ Hz}$ is one vibration per second; $1 \text{ kilohertz (kHz)}$ is a thousand vibrations per second. Frequency determines the pitch or "sharpness" of a sound. Higher frequency means higher pitch. Humans can typically generate and hear sounds in the range of 20 Hz to $20 \text{ kHz}$. Deep Hum: Approximately $200 \text{ Hz}$. Cow Moo: Around $1 \text{ kHz}$. Cat Meow: About $4 \text{ kHz}$. Metallic Spoon Drop: Sharp sound containing frequencies up to about $8 \text{ kHz}$. Musical Scale (Sa-Re-Ga-Ma...): Each note corresponds to a specific, memorized frequency; if the first 'Sa' is $250 \text{ Hz}$, the last 'Sa' is approximately double that, at $520 \text{ Hz}$. Strings (Guitars): A simple way to create air vibrations is by using strings, specifically strong ones, often made of metal. The shorter the string, the higher the frequency (and pitch) of the sound it produces. A guitar works by using fingers to change the vibrating length of the string, thereby changing the frequency/note. Air Columns (Flutes): Hollow tubes allow the air inside to vibrate and generate sounds. The longer the air column, the lower the frequency of the sound. A flute works by placing fingers at different points to change the length of the air column, creating different musical notes. This effect is also noticeable when filling a water bottle: as the air column shortens, the sound becomes sharper (higher pitch). Speakers use a combination of a permanent magnet and an electromagnet to convert electrical signals into sound vibrations. Permanent Magnet: Made of magnetic materials (like iron or nickel), it has a fixed magnetic field with a North and South pole. Same poles repel; opposite poles attract. Electromagnet (The Copper Coil): A copper coil is wound and attached to a drum-like sheet (cone). When the coil carries an electric current, it behaves like a magnet itself, creating an electromagnet. If the current's direction changes, the electromagnet's magnetic field direction (its North and South poles) also changes. Creating Vibration (Sound): The electromagnet is placed next to the permanent magnet. The circuitry supplies a current that switches direction at the desired sound frequency. When the electromagnet's pole is opposite to the permanent magnet's pole, they attract (pull towards each other). When the poles line up (are the same), they repel (push apart). Since the permanent magnet is static, the electromagnet is the one that moves. This continuous push and pull vibrates the attached drum sheet, creating the necessary disturbance (sound wave) in the air molecules. Examples of Sound FrequenciesCreating Musical SoundsThe Physics Behind Speakers: Magnetic Vocal Chords
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2026/01/092 分