What is the Speed if visible light in a vacuum?
it should be 3x10^8 m s^(-1). here is the calculation:
we have known that the refractive index of vacuum is 1,
by n= v/c ( n stands for refractive index of medium, v stands
for the speed of light in medium, c stands for speed of light
constant)
1=v/3X10^8 m s^(-1)
v=
therefore, speed of light in vacuum is 3x10^8 m s^(-1)
actually, all light ray in electromagnetic spectrum have same
speed in vacuum