Question

When current flows in a wire I know that the charge itself moves very very slowly. But I aslo know the signal generated from the charges hitting each other is almost the speed of light.
I wanted to know, is the magnetic field generated by the "Signal"'s existence or is it form the actual movement of the charges?

Answer 1

@Carl_Pham
@ghazi
@Shane_B

Answer 2

well charges move under the drift of electric field that electric field moves at almost speed of light, now the field generated due to that movement is not by any signal it is because of energy itself dissipated by charge because concept of field is also very vague, when you will dig deeper there is nothing that makes field but there is something that occupies a space causing force , concept of field is vague to me too , but i am pretty sure that magnetic field is generated by changing current , which further induces a current due to changing magnetic field which unfortunately opposes sometimes , like in case of electric motors (back emf) so yes , magnetic field is there due to changing current and then due to induced signal too :) sorry if it confuses you :)

Answer 3

My answer would have probably been even more confusing but I don't fully understand it either. I don't think anyone has a true understanding of what actually generates the field or what the field really is...they only know what causes it and the resulting effects.

Physics books just tell you that it just (magically) forms when there is a flow of electric charges...and collapses when the flow stops...and how to calculate its strength. I haven't found a book yet that explains much further than that.

Answer 4

@Shane_B @ghazi

Do you all think the magnetic field "forming" is as fast or close to the speed of the signal?

Answer 5

Or is it much slower than that?

Answer 6

True that all we know is that B is formed where there is a change in I.
But now... How fast do you think that "B"'s formation is?

Answer 7

B is never formed at the speed of light its way too slow

Answer 8

it basically depends on the speed of changing magnitude of current

Answer 9

Wow.
Not as fast or close to the speed of light, wow! Hows fast do you think B is formed?

Answer 10

Could you possibly give an example?

Answer 11

well it totally depends on the speed of changing magnitude , or the movement, by the even if you are able to see the change at the speed of light, what is the significance in that?

Answer 12

So the change is almost at the speed of light right? That would mean it could form quickly?
Since its mostly depending on the "change".

Answer 13

current flows due to change in potential and change in potential depends on rate of change of magnetic flux (farday's law) so it depends basically on the change :)

Answer 14

Ok, and that change is superfast :P
So the magnetic field is generated super fast I guess...

Answer 15

yep, from that point of view its very fast

Answer 16

So we can say that they are some what equal in speed.
The magnetic field + The signal's speed throughout a conductor.

Answer 17

just take a basic example of propagation of electromagnetic wave , that travels at the speed of light

Answer 18

The thing is electromagnetism and their examples are the most complicated field for me in classical physics right now... So I need to understand how C-EMF/EMF and circuits B field from current and what not works... In order for me to compare...

Answer 19

But knowing that the magnetic field(B) is formed pretty fast because the change is close to the speed of light is what I needed to know for now...

Answer 20

So thank you guys for all the help!

Answer 21

okay well formation of magnetic field is not that close to speed of light but still very fast and one thing that i am stuck is, what is the consequence of knowing the speed of formation of magnetic field ?

Answer 22

"what is the consequence of knowing the speed of formation of magnetic field ?"
Do you mean whats the point of knowing that?

Answer 23

exactly, how is it significant , point and reason behind knowing that?

Answer 24

Ok this is going to be a long explanation so this might take time!

Answer 25

its okay just in a line , what is the reason , if its significant then you must know :D even if its not still strive to know :D

Answer 26

Ok, I want to study change in magnetic fields, and how they create C-EMF.

Answer 27

Basic effects in a circuit.
I want to understand what is exactly going on, when, how, etc...

Answer 28

well faraday's law states that and even experimentally you can see that \[e= \frac{ -d \phi }{ dt }\] there is induced emf as soon as magnetic field changes

Answer 29

I know that this question is not common but I was thinking about it a lot lately.

Answer 30

current flows due to potential difference and flow of current causes magnetic field too, that is why pair of wires in domestic purpose is twisted to reduce that loss , and it is not considerable, so it depends on the scale of measurement

Answer 31

Yea.
I wanted to know the rate of that change, the amount of EMF being generated, the current that is being flown, and how long does it take for all that to reach zero as well...
How long does it take to re-shape(turn on) everything back again. How fast B is formed.

Answer 32

Its more of a research that I'm taking step by step.

Answer 33

Thanks again @ghazi
and you too @Shane_B!

Answer 34

you are welcome :D and as soon as you will read a bit more you will be fine :) dont worry , but do imagine and do think :D thats perfect

Answer 35

@ghazi
What laws do I look at the most to understand?
Faraday, Lenz? Only?

Answer 36

there are a few more laws but try to visualize them too

Answer 37

I will... Could you spare me the names of the necessary laws I need to perfectly understand this topic?

Answer 38

krichoff's voltage and current law, faraday's law, lenz's law and lorentz law these are few fundamental laws that you have to keep in mind and try to see them

Answer 39

@ghazi @Shane_B
When I studied C-EME, I noticed in a 12V DC motor running would generate a C-EMF of 10V.
How can the motor operate and have the same speed as it started with low C-EMF or(0)?

Another thing:
In this simple motor:


When the coil changes poles(N>S>N>S) by changing its flow direction would the C-EMF during that process of "change" = 0?

Generally I believe that C-EMF exists in a motor, but at a constant value. It can start at a value and drop again to zero. Then goes back up again and drops to zero and etc...