Moving charges

[Ali Lama]

I have been confused about moving charges create circular magnetic fields around it.

So if I have an electron moving into screen away from me, it will have a circular magnetic field that is clockwise.

Another electron parallel to the above electron coming out of the screen towards me will have a circular magnetic field that is counterclockwise.

So their magnetic field join instead of against each other.  

Do the charges repel as the consequence of their magnetic field joining?

I assume the charges repel each other to my understanding. Which implies they prefer not have a joined magnetic field.  What is missing in the picture that I have in my head? 

Thanks. 

[studiot]

6 hours ago, Ali Lama said:

I have been confused about moving charges create circular magnetic fields around it.

So if I have an electron moving into screen away from me, it will have a circular magnetic field that is clockwise.

Another electron parallel to the above electron coming out of the screen towards me will have a circular magnetic field that is counterclockwise.

So their magnetic field join instead of against each other.  

Do the charges repel as the consequence of their magnetic field joining?

I assume the charges repel each other to my understanding. Which implies they prefer not have a joined magnetic field.  What is missing in the picture that I have in my head? 

Thanks. 

 

Some basics may help here.

 

Firstly if you only have one electron going each way, they will soon pass each other and you will not see much effect.

Of course there will be no magnetic field in front of either moving charge!

You need a regular  stream of them and, to begin with, only consider what happens after the current has been flowing for a long time.
This is known as 'steady state' conditions.
Consideration of the start or end or other change to the stream is much more complicated.

it is often not helpful to consider an electric current as a moving bunch of individual charges, just a current will do.

However, having said that,

When moving the charges generate two fields.
An electric field and a magnetic field.

It is the electric field that is responsible for the attractive/repulsive force between the charges.
This force is always there and in particular when the charges are not moving.

When the charges are not moving, there is no magnetic field.

Also when the magnetic fields are due to (equal) currents running parallel but in the oppsite directions (called anti parallel)
The fields cancel between the wires but form continuous loops round both.

 

Edited October 24, 2019 by studiot

[swansont]

7 hours ago, Ali Lama said:

I have been confused about moving charges create circular magnetic fields around it.

So if I have an electron moving into screen away from me, it will have a circular magnetic field that is clockwise.

Another electron parallel to the above electron coming out of the screen towards me will have a circular magnetic field that is counterclockwise.

As studiot implies, it might be better to look at current rather than individual charges. Also, you have your directions reversed. The right-hand rule assumes positive current. Electrons moving onto the screen is like a positive current moving out, which will give you a counter-clockwise field.

 

49 minutes ago, studiot said:

 Of course there will be no magnetic field in front of either moving charge!

No field directly in front, i.e. on the x-axis for motion in the x direction. 

[studiot]

1 hour ago, swansont said:

Also, you have your directions reversed. The right-hand rule assumes positive current. Electrons moving onto the screen is like a positive current moving out, which will give you a counter-clockwise field.

Really good point.

@Ali Lama, I hope you are not somehwere where they insist on teaching 'electron flow' as the direction of current.

The standard convention is that current flows from positive to negative (what swansont called positive current).

Nearly all the equations of Physics follow this convention, so it is best to stick with it.

[Ali Lama]

To my knowledge here is magnetic field due to parallel moving charges ( conventional current)  going opposite way as in a coil.  Is there attractive force or repulsive force between the two?

 

 

 Imagine two streams of identical charges moving (anti-parallel, moving in parallel and opposite direction) in a vacuum. The two streams are close enough to each other that both the magnetic field and electric field are present. In their own frame of reference, there is an electric field of repulsion and a magnetic field of attraction. Which field will win? :-)

 

 

[swansont]

I don't recall all the details off the top of my head, but this is an effect seen in charged particle and ion beams. It's called a pinch, because the effect can bunch the particles together. Moving charges create the circular magnetic field, which is perpendicular to the current, and creates a force that "pinches" the particles into a tighter beam.

The strength of the field and the magnetic force depend on the speed of the particles, so attraction vs repulsion winning is going to depend on how fast the particles are moving.

[Ali Lama]

3 minutes ago, swansont said:

I don't recall all the details off the top of my head, but this is an effect seen in charged particle and ion beams. It's called a pinch, because the effect can bunch the particles together. Moving charges create the circular magnetic field, which is perpendicular to the current, and creates a force that "pinches" the particles into a tighter beam.

The strength of the field and the magnetic force depend on the speed of the particles, so attraction vs repulsion winning is going to depend on how fast the particles are moving.

You are the first human being that stayed on the topic.  And thank you for your answer and awareness. 

[swansont]

You might want to look into this some more; pinching is for a somewhat different set of conditions, but the general principles will still apply.