What is the speed of light in a perfect world (vacuum)?

What is the speed of light in a perfect world (vacuum)?

• A. 299,792,458 meters per second
• B. 300,000,000 meters per second
• C. 984,300,000 feet per second
• D. 186,000 miles per second

Answer: (B)

Light travels in vacuum at a universal speed, denoted c. In the SI system, c is defined to be exactly 299,792,458 meters per second. This exact value comes from defining the meter as the distance light covers in vacuum in 1/299,792,458 of a second, so c becomes a fixed constant rather than a measured quantity. People often use 3.00×10^8 m/s as a convenient approximation, and you’ll see rounded conversions in feet or miles per second, but the precise figure is 299,792,458 m/s. In a medium, light slows down depending on the material’s refractive index, but in a perfect vacuum it takes off at this exact speed.

Light travels in vacuum at a universal speed, denoted c. In the SI system, c is defined to be exactly 299,792,458 meters per second. This exact value comes from defining the meter as the distance light covers in vacuum in 1/299,792,458 of a second, so c becomes a fixed constant rather than a measured quantity. People often use 3.00×10^8 m/s as a convenient approximation, and you’ll see rounded conversions in feet or miles per second, but the precise figure is 299,792,458 m/s. In a medium, light slows down depending on the material’s refractive index, but in a perfect vacuum it takes off at this exact speed.