For some physics students, the concept of a particle travelling faster than
the speed of light holds endless fascination, and Cherenkov radiation is a
visible consequence of a charged particle travelling through a medium at
locally superluminal velocities. The Heaviside--Feynman equations for
calculating the magnetic and electric fields of a moving charge have been known
for many decades, but it is only recently that the computing power to plot the
fields of such a particle has become readily available for student use. This
article investigates and illustrates the calculation of Maxwell's D field in
homogeneous isotropic media for arbitrary, including superluminal, constant
velocity, and uses the results as a basis for discussing energy transfer in the
electromagnetic field.Comment: 18 pages, 8 figures, 2 MATLAB listings. Version 2: Corrected display
for letter paper format. Added publication info. Version 3: Corrected typos
in Eqs. 5, 8, 1
