主要差异-波长与周期

波长和周期是两种不同但相关的波的性质。波长和周期之间的主要区别在于，波长是波上两个连续的同相点之间的最短距离，而周期是在给定点上发生完全振荡所需的时间。

什么是波长(wavelength)？

波由振荡组成。如果你上下摆动绳子的一端，如下图所示，“摆动”沿着绳子移动。为了沿着绳子传输摆动，绳子上的每个粒子都应该上下移动。例如，在下图所示的时间，A处的粒子处于其上下运动的最高位置（峰值）。由于波是向右传播的，一个稍微偏右的粒子应该在向上的过程中（这样过一会儿，它就会达到峰值）。这是粒子在B的情况。C处的粒子也会上升，比B处的粒子快一点（当它达到同样的水平时，速度会减慢到B的速度）。

Making waves on a rope

A particle at A’ is also at the peak position. A particle at B’ is on the same stage (or “phase”) of its up-down motion as the particle at B. Similarly, the particles at C and C’ are also at the same stage of their up-down motion. The shortest distance between two adjacent points on a wave that are in the same phase is called a wavelength. A wavelength is often denoted by the greek letter lambda (). So for this diagram, the distances  . This distance is marked on the diagram in green arrows. Note that the distance between two peaks or troughs on a wave is one wavelength.

对于由压缩波和稀疏波组成的纵波，波长等于两个相邻压缩波或稀疏波之间的最短距离。如下图所示：

Wavelength in a longitudinal wave

电磁波不是由通过物理振荡来传播电磁波的粒子组成的。因此，对于电磁波，波长是电场在同一相位的两点之间的最短距离。一般来说，如果绘制位移图作为位置的函数，那么图上两个峰值或两个波谷之间的距离将表示一个波长：

Wavelength depicted on a graph of displacement vs. position

因为波长是长度的量度单位，所以它以米为单位。

什么是期间(period)？

As mentioned before, waves c***ist of oscillati***. The time taken to complete one oscillation is called the period. Period is often denoted as  . If you c***ider the displacement of an individual point over an interval of time and plot a graph of how the displacement varies as a function of time, then one period is represented by the distance between two peaks or two troughs. This is shown in the graph shown below. Since period measures an interval of time, it is measured in units of seconds.

Period depicted on a graph of displacement vs. time

The reciprocal of the period is known as the frequency (). That is,

Frequency gives the number of complete oscillati*** per unit time, and it is measured in units of hertz (Hz). For example, the frequency of the musical note “middle C” is about 261.6 Hz. This means that in order to produce this note, particles must vibrate so that each complete vibration of one of these particles takes .

The period of a wave and its wavelength are related by the speed of the wave. During one period, the wave travels a distance of one wavelength (the position of peaks and troughs at a given time on a wave would be identical to the position of peaks and troughs one period later—each peak has travelled to the position that was occupied by the previous peak one period ago). Therefore, if the speed of the wave is  , then:

波长(wavelength)和期间(period)的区别

定义

波长是振荡同相的波上两个连续点之间的最短距离。

周期是完成一次完整振荡所需的时间。

单位

波长是距离的量度。因此，它有国际单位制米。

周期是对时间间隔的度量。因此，它有秒的国际单位制。

图形描绘

波长由位移与位置图中两个连续峰/谷之间的距离给出。

周期由位移与时间关系图中两个连续峰值之间的距离给出。

Image Courtesy

“Wave in a rope.” by CK-12 Foundation (File:High School Chemistry.pdf, page 178) [CC BY-SA 3.0], via Wikimedia Comm*** (Modified)

四次泛音或五次谐波。Lookang（自己的作品）[公共领域]，通过Wikimedia Comm***的“随机分子表示”（修改）