📚 Sound and Hearing Revision | 声音与听觉备考专项
Welcome to the Year 10 Eduqas Physics revision guide for Sound and Hearing. This topic explores how spoken communication (voice) and the sense of hearing connect to the physics of waves. You will learn how sound vibrations are produced, how they travel, and how our ears detect them. Understanding these concepts is essential for both your exams and real‑world applications, from musical instruments to medical ultrasound.
欢迎来到 Year 10 Eduqas 物理“声音与听觉”备考专题。本主题将口语表达（声音的发出）与听觉感知同波动物理学紧密连接。你将学习声振动如何产生、如何传播以及人耳如何探测这些振动。理解这些概念不仅对你的考试至关重要，还有助于你理解从乐器到医用超声的真实世界应用。
1. Production of Sound | 声音的产生
Sound is produced whenever an object vibrates. In speech, our vocal cords vibrate as air is forced past them from the lungs. Pluck a guitar string and it vibrates; strike a drum skin and it moves back and forth. These vibrations push against the surrounding air, creating alternating regions of high and low pressure called compressions and rarefactions.
声音由物体的振动产生。说话时，肺部的气流冲击声带使其振动。拨动吉他琴弦，琴弦振动；敲击鼓面，鼓皮来回运动。这些振动推动周围的空气，形成交替的高压区（密部）和低压区（疏部），即压缩与稀疏。
The frequency of the vibration determines the pitch we hear: rapid vibrations produce high‑pitched sounds, while slower vibrations give low‑pitched sounds. The amplitude of the vibration controls loudness – bigger vibrations make louder sounds.
振动的频率决定了我们听到的音调：快速振动产生高音调的声音，较慢的振动产生低音调的声音。振幅控制响度——振幅越大，声音越响。
2. Nature of Sound Waves | 声波的本质
Sound waves are longitudinal waves. In a longitudinal wave the particle oscillations are parallel to the direction of energy transfer. Air molecules move back and forth along the line of travel, forming compression and rarefaction regions.
声波是纵波。在纵波中，介质粒子的振动方向与能量传递方向平行。空气分子沿传播方向来回移动，形成密部和疏部区域。
Because sound relies on particle vibrations, it cannot travel through a vacuum. There are no particles to transmit the oscillation. This is why astronauts in space must use radios to communicate – sound cannot cross the emptiness of space.
由于声音依赖粒子振动，它不能在真空中传播。没有粒子来传递振动。这就是为什么太空中的宇航员必须使用无线电交流——声音无法跨越真空。
We model sound waves on an oscilloscope display as transverse‑looking waveforms, but remember the true oscillation is longitudinal. The waveform shows how pressure varies with time.
我们在示波器上将声波显示为看似横波的波形，但请记住真实的振动是纵向的。波形表示的是压力随时间的变化。
3. Key Properties: Frequency, Amplitude and Wavelength | 关键特性：频率、振幅与波长
Three fundamental properties describe any sound wave:
描述任意声波有三个基本特性：
Frequency (f) – number of complete vibrations per second, measured in hertz (Hz). The human range is roughly 20 Hz to 20 000 Hz. 频率（f）——每秒完整振动的次数，单位赫兹（Hz）。人耳听觉范围大约为20 Hz到20 000 Hz。
Amplitude – maximum displacement from the undisturbed position. For sound, this corresponds to the maximum pressure change and is perceived as loudness. 振幅——偏离平衡位置的最大位移。对声音而言，它对应最大的压力变化，感知为响度。
Wavelength (λ) – distance between two consecutive compressions (or two rarefactions), measured in metres. 波长（λ）——两个相邻密部（或疏部）之间的距离，单位为米。
On an oscilloscope trace, a higher frequency shows more waves across the screen, while a larger amplitude shows taller peaks.
在示波器轨迹上，频率越高的波形在屏幕上显示的波数越多；振幅越大则波峰越高。
4. The Wave Equation for Sound | 声波的波动方程
For all waves, including sound, the wave speed, frequency and wavelength are linked by the equation:
对所有波（包括声波），波速、频率和波长满足下列方程：
v = f × λ
v – wave speed in metres per second (m/s) v ——波速，单位米/秒（m/s）
f – frequency in hertz (Hz) f ——频率，单位赫兹（Hz）
λ – wavelength in metres (m) λ ——波长，单位米（m）
In air at room temperature, the speed of sound is approximately 340 m/s. That speed stays constant for a given medium, so if frequency doubles, wavelength must halve to keep the product the same.
室温下的空气中，声速约为 340 m/s。在给定介质中波速保持不变，因此如果频率加倍，波长必须减半才能保持乘积不变。
Example: A sound wave has frequency 680 Hz. What is its wavelength in air?(Use v = 340 m/s)
λ = v ÷ f = 340 ÷ 680 = 0.50 m
示例：某一声音频率为 680 Hz，在空气中的波长是多少？（取 v = 340 m/s）
λ = v ÷ f = 340 ÷ 680 = 0.50 m
5. Human Hearing Range | 人耳听觉范围
The typical human ear can detect sounds between 20 Hz and 20 000 Hz (20 kHz). This range decreases with age, especially at high frequencies. Sounds below 20 Hz are called infrasound; vibrations above 20 kHz are ultrasound.
典型人耳能探测 20 Hz 至 20 000 Hz（20 kHz）的声音。这个范围随年龄增长而缩小，尤其是高频部分。低于 20 Hz 的声音称为次声波；高于 20 kHz 的振动称为超声波。
Different animals have very different hearing ranges. Bats and dolphins can hear ultrasound well above 100 kHz, which they use for echolocation. Elephants can detect infrasound, enabling them to communicate over several kilometres.
不同动物的听觉范围差异很大。蝙蝠和海豚能听见远高于 100 kHz 的超声波，用来进行回声定位。大象能探测次声波，因此可在数公里外进行交流。
6. Structure of the Ear and Hearing | 耳朵的结构与听觉
Our ability to hear relies on the ear converting sound vibrations into electrical signals for the brain. The main parts and their roles are:
我们的听觉依赖于将声音振动转换为大脑可接收的电信号。耳朵的主要部分及其功能如下：
| Ear structure 结构 | Function 功能 |
|---|---|
| Pinna (outer ear) 耳廓 | Collects sound waves and directs them into the ear canal. 收集声波并导入耳道。 |
| Eardrum 鼓膜 | Thin membrane that vibrates when sound waves hit it. 薄膜，受到声波撞击时产生振动。 |
| Ossicles (hammer, anvil, stirrup) 听小骨 | Three tiny bones that amplify the vibrations and transmit them to the cochlea. 三块小骨放大振动并传至耳蜗。 |
| Cochlea 耳蜗 | Fluid‑filled spiral that converts vibrations into electrical impulses via hair cells. 充满液体的螺旋结构，通过毛细胞将振动转为电脉冲。 |
| Auditory nerve 听神经 | Carries electrical signals to the brain for interpretation. 将电信号传至大脑进行解读。 |
Damage to any of these parts can cause hearing loss. For example, prolonged exposure to loud sound can destroy hair cells in the cochlea – these do not regenerate.
其中任何一部分受损都可能导致听力下降。例如，长时间暴露于响亮的噪声会破坏耳蜗内的毛细胞，而这些细胞无法再生。
7. Ultrasound and Infrasound | 超声波与次声波
Ultrasound (f > 20 000 Hz) is used in medicine to image a foetus during pregnancy. A transducer sends ultrasound pulses into the body; when the pulses reach boundaries between tissues, some is reflected. The time delay and strength of echoes are used to build an image.
超声波（f > 20 000 Hz）在医学中用于孕期胎儿成像。换能器向体内发射超声波脉冲；当脉冲遇到组织边界时，部分被反射。利用回声的时间延迟和强度构建图像。
Ultrasound is preferred over X‑rays because it does not use ionising radiation, making it safer for the developing baby. It is also used in sonar for underwater mapping and in industrial flaw detection.
超声波优于X射线检查，因为它不使用电离辐射，对正在发育的胎儿更安全。它还用于水下测绘的声纳以及工业探伤。
Infrasound (f < 20 Hz) is produced by earthquakes, volcanic eruptions and heavy machinery. While humans cannot hear it, we may feel it as a throbbing sensation. Scientists use infrasound detectors to monitor natural events.
次声波（f < 20 Hz）由地震、火山爆发和重型机械产生。人类无法听见，但可能会感受到一种搏动感。科学家利用次声波探测器监测自然事件。
8. Echo and Reflection of Sound | 回声与声音的反射
When sound waves strike a large, hard surface, they can be reflected back as an echo. The reflected wave obeys the law of reflection: angle of incidence equals angle of reflection.
当声波撞击大而硬的表面时，会被反射回来形成回声。反射波遵循反射定律：入射角等于反射角。
For an echo to be heard as a distinct repetition, the time delay must be at least 0.1 s. Since sound travels 34 m in 0.1 s, the reflecting surface must be at least 17 m away for the round trip. In smaller rooms, the reflected sound arrives too quickly and blends with the original sound, creating reverberation rather than a clear echo.
要听到清晰可辨的回声，时间延迟至少需要 0.1 秒。声音在 0.1 秒内传播约 34 米，因此反射面至少要在 17 米以外（往返）。在较小的房间内，反射声到达太快，与原声混合，形成的是混响而非清晰的回声。
o return, the depth of the sea or a shoal of fish can be determined using d = (v × t) / 2.
回声原理用于声纳计算距离。通过测量超声波脉冲返回的时间，利用 d = (v × t) / 2 即可确定海水深度或鱼群位置。
9. Sound in Different Media | 声音在不同介质中的传播
Sound travels fastest in solids, slower in liquids and slowest in gases. This is because particles are closest together in solids, enabling vibrations to be passed on more rapidly. In a gas the particles are widely spaced, so energy transfer takes longer.
声音在固体中传播最快，液体中较慢，气体中最慢。这是因为固体中粒子的间距最小，振动能更迅速地传递。气体中粒子的间隔很大，能量传递所需时间更长。
The speed of sound in air is roughly 340 m/s at 20 °C. In water it is about 1500 m/s, and in steel it can reach 5000 m/s. Temperature also affects speed: warmer air transmits sound slightly faster because the particles have more kinetic energy.
在 20 °C 的空气中，声速约为 340 m/s；在水中约为 1500 m/s；在钢中可高达 5000 m/s。温度也会影响速度：温暖空气中声音传播略快，因为粒子具有更大的动能。
A useful experiment to demonstrate this is the 'string telephone' – two cups joined by a taut string. Sound vibrations travel along the string (solid) rather than through the air, so speech can be heard clearly over several metres.
一个有用的演示实验是“纸杯电话”——两个纸杯由一根拉紧的绳子连接。声音振动沿着绳子（固体）传播，而不是通过空气，因此可以在数米外清晰地听到说话声。
10. Measuring the Speed of Sound | 测量声速
the speed of sound in air using an echo method. Students stand a known distance (e.g., 100 er in time with the returning echo. By measuring the time for multiple echoes (say 10 clap‑echo cycles) and using speed = distance / time, an accurate value can be found.
一个经典的学校实验室实验利用回声法测量空气中的声速。学生站在离一面大墙已知距离（例如 100 m）处，用两块木块拍击，使其节奏与回声返回的节奏同步。通过测量多次回声（例如 10 个拍击‑回声循环）的时间，利用速度 = 距离/时间，可以求出较准确的值。
Alternatively, a dual‑ me delay between the two waveforms and the microphone separation give v = distance / time.
或者，可使用双通道示波器。一个麦克风置于声源附近，另一个放在远处。利用两个波形之间的时间延迟以及麦克风之间的距离，由 v = 距离/时间 求出声速。
In Eduqas questions, you may be asked to describe such an experiment, state the measurements, and suggest improvements to reduce uncertainty, such as using a larger distance to reduce timing errors.
在 Eduqas 考题中，可能要求你描述这类实验，列出所需测量量，并提出减少不确定性的改进方法，例如使用更大的距离以减小计时误差。
11. Real‑World Applications and Hearing Protection | 实际应用与听力保护
Knowledge of sound and hearing has led to a wide range of technologies and safety measures. Ultrasound is used not only for prenatal scans but also in physiotherapy to treat deep tissue injuries. In industry, ultrasonic cleaners remove dirt from delicate items like jewelry using high‑frequency vibrations in a liquid.
对声音与听觉的理解催生了广泛的技术与安全措施。超声波不仅用于产前扫描，还用于物理治疗以处理深层组织损伤。工业中，超声波清洗器利用液体中的高频振动去除珠宝等精细物件的污垢。
Understanding hearing ranges has helped design hearing aids that amplify specific frequencies for people with hearing loss. Noise‑cancelling headphones generate sound waves 180° out of phase to cancel unwanted background noise – a direct application of superposition.
对听觉范围的理解帮助设计了助听器，能针对听力受损者的需求放大特定频率。降噪耳机产生相位差 180° 的声波，抵消不需要的背景噪声——这是叠加原理的直接应用。
Hearing protection is crucial. Prolonged exposure to sound levels above 85 dB can cause permanent damage. Using ear defenders in loud environments, keeping volume low on personal audio devices, and following workplace noise regulations all help preserve our sense of hearing.
听力保护至关重要。长时间暴露在 85 分贝以上的声级中会造成永久性损伤。在嘈杂环境中使用护耳器、将个人音频设备的音量调低以及遵守工作场所的噪声法规，都有助于保护我们的听觉。
Published by TutorHao | Physics Revision Series | aleveler.com
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