As a domain expert in the field of physics, particularly in wave mechanics, I can provide a detailed explanation of what changes when a wave is reflected. When a wave encounters a boundary or an obstacle that it cannot pass through, a reflection occurs. The changes that occur during reflection can include: 1. Direction: The most noticeable change is the direction of the wave. The angle of incidence is equal to the angle of reflection, following the law of reflection. 2. Amplitude: Depending on the medium and the nature of the boundary, the amplitude of the wave may change. If the medium is lossless, the amplitude remains the same. However, if there is energy loss due to the medium's properties or the nature of the boundary, the amplitude of the reflected wave may be less than that of the incident wave. 3. Frequency: The frequency of the wave does not change upon reflection. The reflected wave has the same frequency as the incident wave because it is still the same wave just traveling in a different direction. 4. Phase: The phase of the wave might change depending on the boundary conditions. For instance, if the wave encounters a "hard" boundary that does not allow for any penetration, the phase of the reflected wave might be reversed (180 degrees out of phase) compared to the incident wave. 5. Polarization: For electromagnetic waves, the polarization can change upon reflection, especially if the surface is not smooth or if the wave is not normally incident. 6. Speed: If the wave changes medium upon reflection, its speed can change because different media have different properties that affect wave speed. Here's the translation in Chinese: 当波遇到它无法通过的边界或障碍物时，就会发生反射。反射过程中发生的变化可能包括： 1. 方向：最明显的变化是波的方向。入射角等于反射角，遵循反射定律。 2. 振幅：根据介质和边界的性质，波的振幅可能会发生变化。如果介质没有能量损失，振幅保持不变。然而，如果由于介质的属性或边界的性质导致能量损失，反射波的振幅可能会小于入射波的振幅。 3. 频率：波的频率在反射时不会改变。反射波的频率与入射波的频率相同，因为它仍然是同一个波，只是沿着不同的方向传播。 4. 相位：根据边界条件，波的相位可能会发生变化。例如，如果波遇到一个不允许任何穿透的“硬”边界，反射波的相位可能与入射波相反（相位差180度）。 5. 极化：对于电磁波，反射时极化可能会发生变化，特别是如果表面不平滑或者波的入射不是垂直的。 6. 速度：如果波在反射时改变了介质，其速度可能会改变，因为不同的介质具有不同的属性，这会影响波速。 read more >>

Reflection occurs when a wave bounces from the surface of an obstacle. None of the properties of a wave are changed by reflection. The wavelength, frequency, period and speed are same before and after reflection. The only change is the direction in which the wave is travelling.read more >>