Theoretical problem (no calculations) with electric field from moving charge

In summary, a student is having trouble understanding a concept about electric and magnetic fields in a physics 2 course. They approached their professor for clarification, but still did not understand. The concept in question involves a point charge moving at a relativistic speed, eventually stopping, and the effects of this stop propagating. The student and the professor have different interpretations of what happens to the electric field at a distant observer in this scenario. The professor believes the field at the observer is that of a stationary point charge at the origin, while the student believes the observer would feel the field of a moving charge somewhere left of the origin, with a time delay. The student jokingly asks if they should apply for the professor's job due to their differing interpretations
  • #1
solarboy
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Homework Statement



I'm in a physics 2 (electricity and magnetism) course, and I'm having trouble with something the professor discussed in class. I tried approaching him about it afterwards, but it still didn't make sense to me. I really think he made a mistake here, and I'd like input.
we're discussing magnetism, and as a precursor to that we're discussing electric fields generated by moving charges. so we have a point charge q moving at a relativistic speed v to the right on the x-axis. ( Relativistic effects make the electric field more powerful in directions perpendicular to the x-axis than parallel to the x-axis, but otherwise I don't think the prof mentioned anything that depended on the speed being relativistic- I think I qould have the same problem for non-relativistic speeds.) Fine.
At t=t0, the charge is at some negative point on the x-axis p0 (all space and time coordinates are in a stationary reference frame). at t=t1, the charge is at the origin. at that point, the charge decelerates over the extremely brief period dt to v=0.
we began discussing what happens as the effects of the stop propagate (at the speed of light, of course), and this is where I got lost. we're looking at the field at time t2 at a point Pa which is farther away than c(t2-t1) such that the effect has not has time to reach Pa yet.
My professor's version: at t2, the field within distance c(t2-t1)is that of a stationary point charge at the origin. outside, the information that the charge has stopped moving has not reached Pa yet. therefore, the field at Pa is as though the charge had continued moving, so at t2, the field at Pa is that of a moving point charge at v(t2-t1) on the x-axis. when the information that the charge stopped gets to Pa, it will suddenly shift, in Pa's perspective, from being at a positive point on the x-axis to being at the origin. (he did not discuss any relativistic effects, like changing time or location coordinates, other than the boosted field in the y direction.)
My version: at t2, the field within distance c(t2-t1)is that of a stationary point charge at the origin. outside, the information that the charge has stopped has not reached Pa, but neither has the information that the charge is at the origin reached Pa. therefore, Pa will feel the field of a moving charge somewhere left of the origin and will observe it move, decelerate, and stop at the origin in the same way as it actaully did, just with a time delay.
so should I apply for his job?
 
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  • #2
His job is secure for the moment.

There is an effect called aberration for such a moving charge that makes it so the electric field at a distant observer points ahead to where the charge will be if it keeps moving. Weird but true. This is why the professor says the apparent position of the charge snaps back.
 

1. What is the concept of electric field in relation to moving charge?

The electric field is a physical concept that describes the force exerted on a charged particle by the presence of other charged particles. In the case of a moving charge, the electric field is the force that acts on the charge as it moves through space.

2. How does the electric field from a moving charge differ from that of a stationary charge?

The electric field from a moving charge is different from that of a stationary charge because it not only depends on the charge's magnitude and location, but also on its velocity. This means that the electric field changes as the charge moves, whereas the electric field from a stationary charge remains constant.

3. What is the relationship between electric field and magnetic field in the case of a moving charge?

According to the theory of electromagnetism, a moving charge creates both an electric field and a magnetic field. The two fields are closely related, with the electric field being perpendicular to the magnetic field. This relationship is known as the right-hand rule and is crucial in understanding the behavior of moving charges.

4. How does the electric field from a moving charge affect other charged particles?

The electric field from a moving charge can exert a force on other charged particles, causing them to either attract or repel each other depending on their charges. This force is known as the Coulomb force and is responsible for many phenomena in electricity and magnetism.

5. What are some practical applications of understanding the electric field from a moving charge?

Understanding the electric field from a moving charge is essential in many technological and scientific fields, including electronics, telecommunications, and particle physics. It also plays a crucial role in understanding the behavior of charged particles in electromagnetic fields, such as those found in motors, generators, and transformers.

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