What is the value of the speed of light constant?

• A. C = 3.00 x 10^8 m/s
• B. C = 6.626 x 10^-34 Js
• C. C = 1.60 x 10^-19 C
• D. C = 9.81 m/s^2

Answer: (A)

The speed of light in vacuum, denoted by c, is a universal constant defined exactly as 299,792,458 meters per second. For everyday use, it’s common to round that to 3.00 × 10^8 m/s. This precise value is fixed by how the meter is defined in terms of light travel, so in vacuum light travels at that constant speed no matter the observer’s frame of reference (as long as you’re in inertial motion).

The other numbers correspond to different physical constants: 6.626 × 10^-34 J·s is Planck’s constant, 1.60 × 10^-19 C is the elementary charge, and 9.81 m/s^2 is the acceleration due to gravity. They describe other phenomena, not the speed of light.