## Moving Electric Charge Creating a Magnetic Field

Does a moving charge create a magnetic field?

At first the answer was obvious to me, since I = Q/t then if a charge is moved it is simillar to an electric current, and electric currents create magnetic fields.

However in a conductor, an electric current consists of electrons moving past relatively stationary protons.
So I know there is a physical difference between moving a charge and an electric current.
I am just wondering what the differences are,
my guess is that the faster a charged particle moves the electric field get weaker and the magnetic field gets stronger. But i haven't been able to find anything helpful for my understanding.

If anyone knows of any explantions or concepts to help understand what happens it would be appreciated.

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 Quote by Eldgar Does a moving charge create a magnetic field?
Yes.

 Quote by Eldgar At first the answer was obvious to me, since I = Q/t then if a charge is moved it is simillar to an electric current, and electric currents create magnetic fields.
It's not only similar to an electric current, moving charge is the definition of electric current. So they are the same, only in a conductor, you typically have a whole bunch of electrons moving together, so their magnetic fields add together.

 See my post #25 in http://www.physicsforums.com/showthr...c+force&page=2 and this attachment http://www.physicsforums.com/attachm...6&d=1259869448 showing that the Coulomb field gets weaker, and the magnetic field gets stronger, as the velocity approaches c, where the two opposing forces cancel. Bob S

## Moving Electric Charge Creating a Magnetic Field

 Quote by Bob S See my post #25 in http://www.physicsforums.com/showthr...c+force&page=2 and this attachment http://www.physicsforums.com/attachm...6&d=1259869448 showing that the Coulomb field gets weaker, and the magnetic field gets stronger, as the velocity approaches c, where the two opposing forces cancel. Bob S
I just looked over that paper you wrote....I need to sit down and go through it, but from a first read I think your approach was excellent.

I enjoyed your calculation....very straightforward and well written.

 Recognitions: Gold Member Science Advisor You can look up the Liénard-Wiechert potentials in most textbooks, like Jackson. They will give you the electric and magnetic fields for a charge of arbitrary trajectory. But you will find that you do not get an increase in the magnetic field versus the electric field. Once you have a moving charge, the radiation is electromagnetic waves. The electric and magnetic fields maintain a constant relationship between them. So if the electric field decreases, the magnetic field decreases by the same amount. This can be seen explicitly with either the potential or the field equations.
 In charged particle beams, the charge density of the beam produces a radial electric field that produces a repulsive force on individual particles. See Eqn (4) in Karlheinz Schindl's paper http://cas.web.cern.ch/CAS/Loutraki-...ndl/paper1.pdf Simultaneously, the current of the moving beam produces a magnetic field that produces an attractive force on individual particles. See eqn (8). These two opposing forces are combined in Eqn (9) to (11), cancelling each other as β → 1. The cancellation is proportional to 1/γ2. Space charge forces, both Coulomb and magnetic, are well known in charged particle beams, and cause emittance blow-up in low-β, high-current beams. The two forces cancel for very relativistic beams. Bob S
 Ok, i think i have a better understanding of the concepts, though i dont really understand all of those formulas. If i were to keep it simple and just consider two moving point charges with the same charge and velocity. would the forces be? Electric Force Fe=k(q1 x q2)/d2 Magnetic Force Fm = (k(q1 x q2)/d2)(v2/c2) Net Force FN = (k(q1 x q2)/d2)(1-v2/c2)

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