Constant Moving Charge and Field
Does a charge moving with a constant velocity have both
electric and magnetic field?
Wow, that was an easy question!
Ask for further clarification if that leaves you with questions.
Einstein's wrestling with this same concept led to his development of
the special theory of relativity.
Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
There will be a magnetic effect. The electric field at any point will
change. According to Maxwell's equations, electric field changing over
time will generate a magnetic field. Ampere's Law as adjusted to
include for induction tells us that the integral of magnetic field
around a circle is proportional to the rate of change over time of the
electric flux through that same circle. It also tells us that the
faster the charge at a given location, the greater the magnetic field in
the space round the charge.
Dr. Ken Mellendorf
Illinois Central College
The answer to your question is, "it depends upon how you look at it!" And
understanding that question led to some of the greatest achievements of
In the absence of any external factors :
Situation 1, you are sitting still and observing a charged particle move
past you in a straight line. In such a case you could observe a magnetic
field and an electric field from the charged particle. Both the magnetic
and electric fields at your location would vary with time.
Situation 2, you are moving at the same speed and in the same direction as
the charged particle. Now you will not observe any magnetic field, but you
will observe a constant electric field from the charged particle.
Understanding the importance of reference frames in these two situations is
part of what led first to Maxwell unifying our understanding of electricity,
magnetism and light into a single framework, and eventually leading Einstein
to the theory of special relativity. It is curious to note that his seminal
paper on special relativity contains neither of those words in the title.
Rather it is titled (excuse my rough German translation), "Concerning the
electrodynamics of moving bodies."
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Update: June 2012