# Can someone better explain how motion affects an electric field?

• nhmllr
In summary: Can you see how it applies to your own life?Most other Freshman physics texts are better for learning from. Pick one and use it as an accompaniment.Tipler, Eisberg, and Resnick are all great books, but bear in mind - you may just happen to be one of those whose learning style happens to mesh well with Feynman's teaching style. The way to tell is to do exercises: can you apply what he is teaching? Can you see how it applies to your own life?
nhmllr
I am reading through the Feynman lectures in my spare times (the parts that interest me, anyway). The book and it's explanations are usually high quality, although unfortunately I have come across a very poorly explained part that I cannot understand.

http://www.feynmanlectures.caltech.edu/I_28.html#Ch28-S1

In section 28-2 "Radiation," the book talks about how for an accelerating charge, the field drops off as 1/r instead of 1/r^2. I find the book's explanation confusing though, especially the following sentence (and everything after it):

"Of course, the end of er′ goes on a slight curve, so that its acceleration has two components. One is the transverse piece, because the end of it goes up and down, and the other is a radial piece because it stays on a sphere. It is easy to demonstrate that the latter is much smaller and varies as the inverse square of r when r is very great."

What does he mean by er' curving? I cannot understand this. I also couldn't find anything else online to clarify it. Do you understand what is meant by this?

Thanks

Feynman tended to be somewhat casual in his presentation, so you get passages like the one you are puzzled about.

##\hat e_{r'}## is the unit vector pointing at the apparent position of the charge - so it cannot "go in a curve".
I think he's talking about a line he is drawing on a blackboard at this point, which will be a trajectory for the charge he is considering for the example.

What's important to this discussion is the acceleration of the charge. If the charge changes direction things can get more complicated because changing direction is also an acceleration.
That's really all that's on his mind.

Note:
You should not use the Feynman lectures by themselves for learning physics.
Use them in conjunction with other materials, other texts.

They are not famous for being good for learning from - they are famous for being presented by Richard Feynman. In their day, the lecture series was a failure. These days they are best used after a basic course of physics has been completed - as a way of solidifying your knowledge.

Simon Bridge said:
In their day, the lecture series was a failure.

They were??

Simon Bridge said:
Feynman tended to be somewhat casual in his presentation, so you get passages like the one you are puzzled about.

##\hat e_{r'}## is the unit vector pointing at the apparent position of the charge - so it cannot "go in a curve".
Note:
You should not use the Feynman lectures by themselves for learning physics.
Use them in conjunction with other materials, other texts.

They are not famous for being good for learning from - they are famous for being presented by Richard Feynman. In their day, the lecture series was a failure. These days they are best used after a basic course of physics has been completed - as a way of solidifying your knowledge.

I've heard that before, but I've found them to be pretty helpful and waaaayyy better (and more centralized) at explaining things than most sources. I'm open to suggestion, though. Do you have any better books in mind that would be better for this sort of thing?

HomogenousCow said:
They were??

Haha. Definately they were

cb

HomogenousCow said:
They were??
Failures?

Cosmobrain said:
Haha. Definately they were
cb
For teaching freshman physics - yes. There were all sorts of contributing factors though.

nhmllr said:
I've heard that before, but I've found them to be pretty helpful and waaaayyy better (and more centralized) at explaining things than most sources. I'm open to suggestion, though. Do you have any better books in mind that would be better for this sort of thing?

My copy of the Feynman Lectures had an introduction that included a description of the original reception. Basically, beginners are best taught by people who did not find physics easy when they were starting out.

If you come from a strong physics background they can be great.
Feynman's "take" on teaching physics is something of a "magical mystery tour" and he fills in a lot of the gaps that the regular style of teaching tends to leave (leaving other problems behind - there are no easy answers).

Practically any other Freshman physics text is better for learning from. Pick one and use it as an accompaniment. I've used everything from Tipler to Eisberg & Resnick.

But bear in mind - you may just happen to be one of those whose learning style happens to mesh well with Feynman's teaching style. The way to tell is to do exercises: can you apply what he is teaching?

## 1. How does motion affect an electric field?

Motion can cause changes in the electric field by creating a magnetic field. When charged particles are in motion, they create a magnetic field that interacts with the existing electric field. This can cause the electric field to change in strength and direction.

## 2. Can motion generate an electric field?

Yes, motion can generate an electric field in certain situations. This is known as electromagnetic induction, where a changing magnetic field creates an electric field. This is the principle behind generators and electric motors.

## 3. How does the speed of motion impact the electric field?

The speed of motion can impact the strength of the electric field. According to Maxwell's equations, the strength of the electric field is directly proportional to the speed of the moving charged particles. This means that faster motion can result in a stronger electric field.

## 4. Can motion affect the direction of an electric field?

Yes, motion can affect the direction of an electric field. As mentioned earlier, moving charged particles create a magnetic field that interacts with the electric field. This interaction can cause the electric field to change direction, depending on the direction of the motion.

## 5. How does motion affect the behavior of charged particles in an electric field?

Motion can affect the behavior of charged particles in an electric field in various ways. For example, if a charged particle is in motion, it may experience a force from the electric field, causing it to accelerate or change direction. On the other hand, if the charged particle is stationary, it may experience a force from the electric field that keeps it in place.

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