Light travels at the fastest speed in:

The correct answer is Vacuum.

Key Points

• Light travels at the fastest speed in a vacuum because there is no medium to obstruct its propagation.
• The speed of light in a vacuum is approximately 299,792 kilometers per second (or 3 × 10⁸ meters per second).
• This speed is considered the universal constant, often denoted by the symbol ‘c’.
• In other mediums (like air, water, or glass), light slows down due to interactions with the particles of the medium.

Additional Information

• Glass: Light travels slower in glass compared to other mediums due to its higher refractive index. The refractive index of glass typically ranges from 1.5 to 1.9, meaning light slows down significantly when passing through it.
• Water: Water has a refractive index of approximately 1.33. Light slows down when traveling through water compared to air or vacuum due to the density and molecular structure of water.
• Hydrogen: Hydrogen, being a gas, has a lower density compared to liquids or solids. However, light still slows down when passing through hydrogen due to the presence of particles that interact with the light waves.
• Vacuum: A vacuum is a space devoid of matter, and light travels at its fastest speed here because there are no particles to impede or refract its propagation.