Unlike an ocean wave, a wavefront or surface of constant phase is unobservable and undetectable.
和海浪不同，波阵面或固定相平面是不能观测和不能发现的。
As the speed is constant, when the frequency is increased, the wave length will.
因为速度不变，当频率增加时，波长就会减少。
This is a constant-amplitude wave which is essentially the same on the conjugate image plane.
这是一个振幅恒定的波，在共轭的象平面上也是如此。
Ift is treated as a constant, it represents the wave profile at that instant.
若视t为常数，则该式表示这一瞬间的波形。
Ift is treated as a constant, it represents the wave profile at that instant.
若视t为常数，则该式表示这一瞬间的波形。
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