✔ 最佳答案
電磁波真空時的速率是c=299792458m/s
In metric units, the speed of light is exactly 299,792,458 metres per second (1,079,252,848.8 km/h).
速率跟不是真空是有所不同的
The speed of light when it passes through a transparent or translucent material medium, like glass or air, is slower than its speed in a vacuum. The ratio of c to the observed phase velocity is called the refractive index of the medium.
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