Describing Waves | 波的描述

📚 Describing Waves | 波的描述

A wave is a disturbance that transfers energy from one place to another without transferring matter. In CIE A Level Physics, the topic “Describing waves” builds the language used to describe wave motion: displacement, amplitude, wavelength, period, frequency, speed, phase and intensity. You must be able to interpret wave graphs, use the wave equation, distinguish transverse from longitudinal waves, and explain polarisation as evidence for the nature of transverse waves.

波是一种将能量从一个地方传递到另一个地方而不传递物质的扰动。在 CIE A Level 物理中，“波的描述”这一主题建立了描述波动所需的语言：位移、振幅、波长、周期、频率、波速、相位和强度。你必须能够解读波形图、使用波动方程、区分横波与纵波，并解释偏振为何能证明横波的本质。

1. What is a wave? | 什么是波？

A wave is a disturbance that transfers energy from one place to another without transferring matter. When a progressive wave moves through a medium, the particles of the medium oscillate about fixed equilibrium positions and pass energy to their neighbours.

波是一种将能量从一个地方传递到另一个地方而不传递物质的扰动。当行波通过介质传播时，介质中的粒子围绕固定的平衡位置振动，并将能量传递给相邻粒子。

Waves can be mechanical, such as sound waves and water waves, which require a medium, or electromagnetic, such as light and radio waves, which can travel through a vacuum. In progressive waves, energy is carried away from the source; in standing waves, energy is stored between nodes. CIE questions usually focus on progressive waves when describing wave parameters.

波可以是机械波，例如声波和水波，它们需要介质；也可以是电磁波，例如光和无线电波，它们可以在真空中传播。在行波中，能量从波源向外传递；在驻波中，能量储存在波节之间。CIE 试题在描述波参数时通常关注行波。

2. Transverse and longitudinal waves | 横波与纵波

Transverse waves have oscillations perpendicular to the direction of energy transfer. Examples include all electromagnetic waves, waves on a stretched string, and S-waves in earthquakes.

横波的振动方向垂直于能量传递的方向。例如所有电磁波、拉伸弦上的波以及地震中的 S 波。

Longitudinal waves have oscillations parallel to the direction of energy transfer. They consist of compressions and rarefactions. Sound waves in air and P-waves in earthquakes are longitudinal.

纵波的振动方向平行于能量传递的方向。它们由密部和疏部组成。空气中的声波和地震中的 P 波都是纵波。

You should be able to identify these two wave types from diagrams. In a transverse wave diagram, the oscillations are shown as crests and troughs above and below the undisturbed line. In a longitudinal wave diagram, a series of compressed and stretched regions is shown along the direction of travel.

你应该能够从示意图中识别这两种波型。在横波图中，振动表现为未扰动线上下的波峰和波谷。在纵波图中，沿传播方向显示一系列被压缩和被拉伸的区域。

3. Displacement, amplitude and wavelength | 位移、振幅与波长

Displacement of a point on a wave is its distance from the undisturbed position in a particular direction. It can be positive or negative depending on whether the point is above or below the equilibrium position. Amplitude is the maximum displacement from the undisturbed position, so it is always a positive scalar.

波上某点的位移是指它沿某一方向相对于未扰动位置的距离，可正可负。振幅是离开未扰动位置的最大位移，因此始终为正标量。

Wavelength is the shortest distance between two points on a wave that are in phase. For a transverse wave, this is often the distance between adjacent crests or adjacent troughs. For a longitudinal wave, it is the distance between the centres of adjacent compressions or adjacent rarefactions.

波长是波上两个同相点之间的最短距离。对于横波，这通常是相邻波峰或相邻波谷之间的距离。对于纵波，则是相邻密部中心或相邻疏部中心之间的距离。

All these quantities describe the shape of a wave in space. They do not depend on time; a wave graph at one instant shows the spatial pattern.

所有这些量都描述波在空间中的形状。它们不依赖于时间；某一瞬间的波形图显示的是空间分布模式。

4. Period, frequency and wave speed | 周期、频率与波速

The period T of

Published by TutorHao | A-Level Physics Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）