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 absolute refractive index of a medium is defined as the ratio of the speed of light in vacuum to the speed of light in the medium.
• If the refractive index is less than 1, the speed of light in the medium is greater than the speed of light in vacuum.
• Refractive index values less than 1 are theoretically possible but occur only in specific cases, such as certain engineered materials like metamaterials.
• In normal conditions, natural materials typically have refractive indices greater than or equal to 1.
• The phenomenon of light traveling faster in a medium than in vacuum is tied to specialized optical properties and not observed in everyday transparent media.

Additional Information

• Refractive Index: It is a dimensionless number that describes how light propagates through a medium.
• Vacuum: The standard medium for measuring refractive index, where the speed of light is approximately 299,792 km/s.
• Metamaterials: Engineered materials that can exhibit unusual optical properties, including refractive indices less than 1.
• Speed of Light: Light travels at its maximum speed in a vacuum, and its speed decreases in denser media like glass or water.
• Cherenkov Radiation: A phenomenon where particles travel faster than light in a medium, producing a visible glow, often mistaken for faster-than-light travel but not applicable to vacuum conditions.