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A moving charge produces a magnetic field...this happens why and how

A moving charge produces a magnetic field...this happens why and how

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2 Answers

Rinkoo Gupta
askIITians Faculty 80 Points
7 years ago
A charged particle moving without acceleration produces an electricas well as a magnetic field.
Electric and magnetic fields are what theelectromagneticfield 'looks like' from a particular (inertial) frame of reference.

Take a charged particle: In its rest frame, it appears to generate an electric field only and no magnetic field at all. From a different frame of reference (in particular one in relative motion), we'll see the charge moving, thus a current which generates a magnetic field as well.

This does not mean that setting the particle in motion somehow flipped a switch within the particle - rather, it's an artifact of our choice of frame of reference: Observers in relative motion will measure different strenghts of electric and magnetic fields the same way they measure different velocities and momenta.

There are however invariants of the electromagnetic field, ie things all observers can agree upon, and in particular

PQ=B?2-E?2=E?·B?

Let's take a nonzero em field withP,Q=0, ieE?2=B?2andE??B?. An example would be a plane electromagnetic wave, which will look like a plane wave for everyone.

Now, letP?0butQ=0. Then, we can find frames of reference where either the electric (in case ofP>0) or the magnetic field (in case ofP<0) vanishes. The rest frame of our charged particle would be such a one.

Thanks & Regards

Rinkoo Gupta

AskIITians Faculty

Vasantha Kumari
askIITians Faculty 38 Points
7 years ago
We know that in special relativity, going from one reference frame to another changes the fields from one type to another. In other words, if you have an electric field but no magnetic field in some frame, if you look in a relatively moving frame there will be a different electric field and now some magnetic field. Likewise if you have a magnetic field but no electrc field in some frame, if you look in a relatively moving frame there will be a different magnetic field and now some electric field. Hence a change in position of a charge such as an electron produces a magnetic field. Hope i have explained precisely as per your question. Thanks & Regards, Vasantha Sivaraj, askIITians faculty

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