Fast medium

The speed at which light travels through different media, such as air, glass, or water, is not a constant. Some media are considered “fast” because light passes through them more quickly than others.

  • Light travels through a vacuum at 299,792 kilometres per second.
  • Light travels at slower speeds through other media. However, it’s important to note that referring to a vacuum as a “medium” is contradictory since a vacuum represents space devoid of matter.
  • Within the Earth’s atmosphere, light can travel at speeds near the speed of light. However, in other cases or through different media, light travels at significantly slower speeds.
  • Understanding whether a medium is considered “fast” or “slow” is valuable in predicting the behaviour of light when it crosses the boundary between different media. As such:
    • When light crosses the boundary from a fast medium to a slower medium, it will bend towards the normal.
    • When light crosses the boundary from a slow medium to a faster medium, the light ray will bend away from the normal.
  • In optics, the “normal” is a line drawn in a ray diagram that is perpendicular, or at a right angle (90 degrees), to the boundary between two media.
  • The phenomenon of light bending when it crosses the boundary between different media is known as refraction.
  • The speed of light in a medium is determined by its refractive index, which is a measure of how much the medium slows down light compared to its speed in a vacuum.

Light travels through different media such as air, glass or water at different speeds.  A fast medium is one through which it passes through more quickly than others.

  • Light travels through a vacuum at 299,792 kilometres per second.
  • Light travels through other media at lower speeds.
  • In some cases, it travels at a speed which is near the speed of light (the speed at which light travels through a vacuum) and in other cases, it travels much more slowly.
  • It is useful to know whether a medium is fast or slow to predict what will happen when light crosses the boundary between one medium and another.
  • so:
  • If light crosses the boundary from a medium in which it travels fast into a material in which it travels more slowly, then it will bend towards the normal.
  • If light crosses the boundary from a medium in which it travels slowly into a material in which it travels more quickly, then the light ray will bend away from the normal.
  • In optics, the normal is a line drawn in a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.