读数
发生了什么
行波以 v = fλ 的速度传播。两列相同的波沿相反方向传播时会叠加：它们的位移直接相加。结果形成驻波：波节处的点始终不动，波腹则以两倍的振幅摆动。这里弦本身就是图像：位移随位置变化，并随时间动起来。
- Wave equationv = fλ
- Travelling wavey = A sin(kx − ωt)
考试大纲
- GCSE Physics AQA 4.6.1wave speed, frequency and wavelength
- A-Level Physics AQA 3.3.1superposition and stationary waves
挑战
先预测：打开两列波时，如果波长减半，弦上能有几个波节？在改变前后各数一数。
波长减半，波节数加倍，因为波节沿着弦每隔半个波长出现一个。
系统地学
GCSE Combined and Separate Science 中讲这个主题的课：先看分步讲解，再做考试风格的题目，每次数字都不同。 课程为英文。
常见问题
How do you calculate wave speed?
Wave speed equals frequency times wavelength, v = fλ. A 2 Hz wave with a 1.5 m wavelength travels at 3 m/s.
What is a standing wave?
Two identical waves travelling in opposite directions add up into a pattern that does not travel. Nodes never move and antinodes oscillate with twice the amplitude.
How far apart are the nodes?
Half a wavelength. So halving the wavelength doubles the number of nodes along the string.
How do I find the wavelength from the speed and frequency?
Rearrange v = fλ to λ = v/f. Sound at 340 m/s with a frequency of 512 Hz has λ = 340 / 512 = 0.664 m, and in a standing wave its nodes would sit 0.332 m apart. Pick Wavelength or Node spacing under Solve for to see each step.