# Why doesn't a charge repel a magnetic field in this example?

• Samson4
In summary, the conversation discusses the behavior of an electron in a magnetic field, including its circular motion and the presence of a magnetic field around the electron itself. It also questions why the electron does not experience a force opposing the original magnetic field, similar to what would happen in a conductor. The conversation also touches on the concept of the electron's own field and its effect on itself, as well as the role of multiple electrons in this scenario. Overall, the conversation delves into the intricacies of the electron's behavior in a magnetic field.
Samson4
The example:
An electron is trapped in a magnetic field. The electron travels along a circle in a clockwise path. It's my understanding that there is a magnetic field around the electron also circulating in a clockwise direction perpendicular to it's path. Now if this electron was in a conductor, the conductor would have a magnetic field opposing the original magnetic field. So, why doesn't the electron?

Samson4 said:
The example:
An electron is trapped in a magnetic field. The electron travels along a circle in a clockwise path. It's my understanding that there is a magnetic field around the electron also circulating in a clockwise direction perpendicular to it's path. Now if this electron was in a conductor, the conductor would have a magnetic field opposing the original magnetic field. So, why doesn't the electron?

View attachment 111533
Does not the electron perform a spiral as a result of what you are saying?

tech99 said:
Does not the electron perform a spiral as a result of what you are saying?
It will spiral if it has a parallel component to it's velocity.

Samson4 said:
The example:
An electron is trapped in a magnetic field. The electron travels along a circle in a clockwise path. It's my understanding that there is a magnetic field around the electron also circulating in a clockwise direction perpendicular to it's path. Now if this electron was in a conductor, the conductor would have a magnetic field opposing the original magnetic field. So, why doesn't the electron?

View attachment 111533
For the case of the loop of wire, the magnetic field inside the loop points in the opposite direction to that outside it. So overall, I don't think it has a force on it.
The single electron does seem to have a resultant force causing it to spiral, because it is acting like a loop edge-on to the magnetic field.

ORF
tech99 said:
For the case of the loop of wire, the magnetic field inside the loop points in the opposite direction to that outside it. So overall, I don't think it has a force on it.
The single electron does seem to have a resultant force causing it to spiral, because it is acting like a loop edge-on to the magnetic field.
On my second point, I don't think I am correct here. The electron has opposite fields above and below it, so presumably these cancel.

Normally, you neglect the effect of a particle's field on itself. If you had more than one electron, then you would have to consider the effect of the electrons' fields on each other.

Samson4
I think the electron did work against its own field when it was accelerated to its present velocity and this energy is now mostly stored in its magnetic field.

Samson4
I see now that the magnetic field of the electron is reinforced on 1 side, according to the left hand rule. This makes since for the electron to curve away from that side without experiencing a net repulsion.

## 1. Why doesn't a charge repel a magnetic field in this example?

The reason a charge does not repel a magnetic field is because magnetic fields are created by moving charges, not stationary charges. In order for a charge to repel a magnetic field, it would have to be in motion.

## 2. Can a charge ever repel a magnetic field?

Yes, a charge can repel a magnetic field if it is in motion. This is because a charge in motion creates a magnetic field, and the two magnetic fields will interact and repel each other.

## 3. What is the difference between an electric field and a magnetic field?

An electric field is created by stationary charges, while a magnetic field is created by moving charges. Electric fields exert forces on other charges, while magnetic fields exert forces on other moving charges.

## 4. Why do magnetic fields only interact with moving charges?

Magnetic fields are created by moving charges, so they only interact with other moving charges. This is because the interaction between two magnetic fields is based on the motion of the charges, not their position.

## 5. How does the strength of a magnetic field affect its interaction with a charge?

The strength of a magnetic field determines the force it exerts on a charge. A stronger magnetic field will exert a greater force on a charge, while a weaker magnetic field will exert a smaller force. However, the direction of the force depends on the direction of the magnetic field and the motion of the charge.

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