主要差異-波長與週期

波長和週期是兩種不同但相關的波的性質。波長和週期之間的主要區別在於，波長是波上兩個連續的同相點之間的最短距離，而週期是在給定點上發生完全振蕩所需的時間。

什麼是波長(wavelength)？

波由振蕩組成。如果你上下擺動繩子的一端，如下圖所示，“擺動”沿著繩子移動。為了沿著繩子傳輸擺動，繩子上的每個粒子都應該上下移動。例如，在下圖所示的時間，A處的粒子處於其上下運動的最高位置（峰值）。由於波是向右傳播的，一個稍微偏右的粒子應該在向上的過程中（這樣過一會兒，它就會達到峰值）。這是粒子在B的情況。C處的粒子也會上升，比B處的粒子快一點（當它達到同樣的水平時，速度會減慢到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.

對於由壓縮波和稀疏波組成的縱波，波長等於兩個相鄰壓縮波或稀疏波之間的最短距離。如下圖所示：

Wavelength in a longitudinal wave

電磁波不是由透過物理振蕩來傳播電磁波的粒子組成的。因此，對於電磁波，波長是電場在同一相位的兩點之間的最短距離。一般來說，如果繪製位移圖作為位置的函式，那麼圖上兩個峰值或兩個波谷之間的距離將表示一個波長：

Wavelength depicted on a graph of displacement vs. position

因為波長是長度的量度單位，所以它以米為單位。

什麼是期間(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:

波長(wavelength)和期間(period)的區別

定義

波長是振蕩同相的波上兩個連續點之間的最短距離。

週期是完成一次完整振蕩所需的時間。

單位

波長是距離的量度。因此，它有國際單位制米。

週期是對時間間隔的度量。因此，它有秒的國際單位制。

圖形描繪

波長由位移與位置圖中兩個連續峰/谷之間的距離給出。

週期由位移與時間關係圖中兩個連續峰值之間的距離給出。

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)

四次泛音或五次諧波。Lookang（自己的作品）[公共領域]，透過Wikimedia Comm***的“隨機分子表示”（修改）