Speed Of Electromagnetic (Em) Field Propagation:
The so-called speed of light is around 2.99792 x 108 m/s. This works out to about 186,282 miles per second (mi/s). The Radio waves, visible light, infrared, ultraviolet, x-rays, and gamma rays all propagate at this speed that Albert Einstein postulated to be similar, no matter from what point of view it is measured.
How quick, exactly, is this? One way to grasp this is to compute how long it would take a ray of light to travel from home plate to the center-field fence in a main league baseball stadium. Most of the ballparks are about 122 m deep to center field; this is quite close to 400 feet (ft). To compute the time t it takes a ray of light to travel that far, we should divide 122 m by 2.99792 x 108 m/s:
t =122/(2.99792 x108)
= 4.07 x 10-7
That is merely a little more than four-tenths of a microsecond (0.4 µs), an unnoticeably short interval of time.
Two things must be noted at this time. At first, remember the principles of important figures. We are justified in going to only three important figures in our result here. Secondly, the units should be consistent with each other to get a meaningful result. Mixing units is a no-no in any computation. It almost always leads to trouble. When we were to take the preceding problem and compute in terms of units without using any numbers at all, this is what we would acquire:
seconds = meters/(meters per second)
s = m/(m/s) = m x s/m
In this computation, meters cancel out, leaving only seconds. Assume, though, that we were to try to make this computation using feet as the figure for the distance from home plate to the center-field fence? We would then acquire little value in undefined units; call them fubars (fb):
fubars = feet/(meters per second)
fb = ft/(m/s) = ft x s/m
Feet do not cancel out meters. Therefore we have invented a new unit, the fubar, which is equal to a foot-second per meter. This unit is fundamentally useless, as would be our numerical result. (As an aside, fubar is an acronym for "fouled up beyond all acknowledgment.")
Always keep in mind to be consistent with units whenever making computations! Whenever in doubt, decrease all the "givens" in a problem to SI units before beginning to make computations. You will then be certain to get an answer in derived SI units and not fubars or gobbledygooks or any other nonsensical things.