It has been shown by experiments on
electromagnetic waves of different wavelengths that this velocity is the
same (independent of wavelength) to within a few metres per second, out
of a value of 3×108 m/s The constancy of the velocity of em waves in
vacuum is so strongly supported by experiments and the actual value is
so well known now that this is used to define a standard of length The great technological importance of electromagnetic waves stems
from their capability to carry energy from one place to another The
radio and TV signals from broadcasting stations carry energy