# Magnetic field lines around electron and wire seem to contradict

• SamRoss
In summary, the direction of magnetic field lines can be determined by using the right-hand rule with the thumb pointing in the direction of the current. However, when thinking about the direction of electron movement in an electric current, the convention is opposite to the direction of positive current flow. This can be attributed to Benjamin Franklin's original convention, although it is not always necessary to think about the motion of electrons when dealing with electric currents.
SamRoss
Gold Member
In the picture below, the direction of the magnetic field lines can be determined by using the right-hand rule with the thumb pointing in the direction of the current.

If we use the right hand rule in the picture below, thinking of the yellow arrow as the current, we would not get the correct direction for the magnetic field.

I'm aware that electrons do not literally spin around like little tops, but they are often depicted as spinning around because they have magnetic fields around them as if they were spinning. I'm curious as to why the electrons would be depicted as spinning around in a direction which would contradict the right-hand rule. Is it because their angular momentum is in this direction (that is, in a direction such that the relationship between it and the magnetic field can be found with a left-hand rule instead)?

What is the charge of the electron, and what is the convention for the direction of charge flow in an electric current?

SamRoss
Nugatory said:
What is the charge of the electron, and what is the convention for the direction of charge flow in an electric current?

I see. So in the first picture I posted, the current is pointing up but the electrons would actually be flowing down. Is that it?

https://xkcd.com/567/
Yes, the direction of positive current flow is opposite to the direction of electron movement.
(And in practice it is almost never helpful or necessary to think about an electric current in terms of moving electrons)

berkeman and SamRoss
SamRoss said:
I see. So in the first picture I posted, the current is pointing up but the electrons would actually be flowing down. Is that it?
You can blame it all on Benjamin Franklin apparently.

SamRoss
Nugatory said:

Loved the comic :)

Nugatory said:
https://xkcd.com/567/
Yes, the direction of positive current flow is opposite to the direction of electron movement.
(And in practice it is almost never helpful or necessary to think about an electric current in terms of moving electrons)
The cartoon is great, but I tend to the opposite opinion concerning the statement. To the contrary I think it's always of great advantage to think about the motion of the conduction electrons relative to the positive ion lattice in a metal when it comes to currents in usual conductors. With this in mind there's almost no more trouble with Faraday's Law of induction in connection with problems like the homopolar generator or the correct relativistic treatment of the current-carrying wire:

https://www.physicsforums.com/insights/homopolar-generator-analytical-example/
https://www.physicsforums.com/insights/relativistic-treatment-of-the-dc-conducting-straight-wire/

## 1. Why do magnetic field lines around an electron and wire seem to contradict?

The apparent contradiction arises because the magnetic field lines around an electron and a wire have different orientations. The magnetic field lines around an electron are circular, while those around a wire are straight. This is due to the different sources of the magnetic field in each case.

## 2. How can a wire have magnetic field lines if it is not a magnet?

While a wire itself may not be a magnet, it can still produce a magnetic field when an electric current flows through it. This is because moving charges (electrons) create a magnetic field, and in a wire, there are many moving charges due to the flow of current.

## 3. Why do magnetic field lines around an electron and wire not follow the same pattern as electric field lines?

Electric field lines and magnetic field lines have different properties and behave differently. Electric field lines originate from positive charges and terminate at negative charges, while magnetic field lines form closed loops around a magnetic source. This is due to the different fundamental forces at play - electric fields are created by electric charges, while magnetic fields are created by moving charges.

## 4. How do magnetic field lines around an electron and wire affect each other?

The magnetic field lines around an electron and wire can interact with each other. When a wire with a current flowing through it is placed near an electron, the magnetic field lines from the wire can affect the circular motion of the electron's magnetic field lines, causing them to bend or distort. This phenomenon is known as the Lorentz force.

## 5. Can the magnetic field lines around an electron and wire ever align with each other?

In some cases, the magnetic field lines around an electron and wire can align with each other. This can happen when the wire is coiled into a solenoid, which creates a strong and uniform magnetic field along its axis. In this case, the circular magnetic field lines around the electron can align with the straight field lines of the solenoid, resulting in a more uniform and stronger magnetic field.

• Electromagnetism
Replies
2
Views
851
• Electromagnetism
Replies
27
Views
1K
• Electromagnetism
Replies
1
Views
1K
• Electromagnetism
Replies
17
Views
1K
• Electromagnetism
Replies
5
Views
943
• Electromagnetism
Replies
7
Views
1K
• Electromagnetism
Replies
7
Views
1K
• Electromagnetism
Replies
73
Views
3K
• Electromagnetism
Replies
15
Views
1K
• Electromagnetism
Replies
2
Views
717