If the absolute refractive index of a medium is less than 1, it means ________.

The correct answer is light travels faster in that medium than in vacuum.

Key Points

• The refractive index of a medium is a measure of how much the speed of light is reduced inside the medium compared to vacuum.
• An absolute refractive index of less than 1 means that light travels faster in that medium than in a vacuum.
• This is because the refractive index (n) is defined as the ratio of the speed of light in vacuum (c) to the speed of light in the medium (v): n = c/v.
• For most materials, the refractive index is greater than 1, meaning light travels slower in those materials than in a vacuum.
• However, if n < 1, it implies that v > c, indicating that the speed of light in that medium is greater than the speed of light in a vacuum.
• This phenomenon is very rare and typically occurs in certain exotic materials with specific optical properties.

 Additional Information

• The medium is a perfect reflector
  • This option suggests that the medium reflects all light that hits it, but this is unrelated to the refractive index being less than 1.
  • Perfect reflectors typically have a high refractive index, indicating that they do not allow light to pass through them.
• The medium absorbs all light
  • This option indicates that the medium does not transmit or reflect light, but instead absorbs it.
  • Absorptive materials usually have a high extinction coefficient, which is a different property from the refractive index.
• Light travels slower in that medium than in vacuum
  • This is true for most materials where the refractive index is greater than 1.
  • If the refractive index is greater than 1, it means light slows down when it enters the medium compared to its speed in a vacuum.