The amplitude of light changes during refraction because refraction is typically accompanied by reflection, leading to a reduction in the transmitted wave's amplitude.
Here's a breakdown of why this happens:
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Reflection and Transmission: When light encounters an interface between two media with different refractive indices (like air and water), some of the light is reflected, and some is transmitted (refracted).
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Energy Conservation: The energy of the incident light must be conserved. This energy is distributed between the reflected and refracted waves.
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Amplitude and Energy: The amplitude of a wave is directly related to its energy. Since some energy is carried away by the reflected wave, the energy (and thus the amplitude) of the refracted wave is less than the amplitude of the incident wave.
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Specific Cases: Complete Refraction: The reference mentions "complete refraction." Hypothetically, if there were a special case where all light was refracted and none reflected, the amplitude could remain theoretically the same (assuming no energy losses within the medium itself). However, this is practically impossible.
Factors Affecting Amplitude Change:
The amount of amplitude change during refraction depends on several factors:
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Angle of Incidence: The angle at which light strikes the interface affects the amount of reflection. At certain angles (like Brewster's angle), reflection can be minimized for a specific polarization.
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Refractive Indices of the Media: The difference in refractive indices between the two media significantly impacts the amount of reflection. A larger difference in refractive indices generally leads to more reflection and a greater reduction in the refracted wave's amplitude.
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Polarization of Light: The polarization of light also plays a role. The amount of reflection varies depending on whether the light is polarized parallel or perpendicular to the plane of incidence.
In summary: Refraction almost always involves some degree of reflection. Because the incident light's energy is split between reflection and refraction, the amplitude of the refracted light is generally lower than that of the incident light. The exact amount of change depends on the angle of incidence, the refractive indices of the media, and the polarization of the light.
