# Why is the magnetic field around a piece of wire circular?

• ihateblackbox
In summary, electric and magnetic fields are created by charged particles. A charged particle has an electric field around it and a moving charged particle creates a magnetic field perpendicular to its direction of movement. In materials, the electrons in orbit around different nuclei can line up to create a macro magnetic field, resulting in ferromagnetic properties. When a voltage is applied to a conductor, charged particles within it tend to move, creating a circular magnetic field. This is because the moving particles have a wave function and momentum, which influences other charges and is seen as the magnetic field. The direction of the magnetic field is defined by the Curl of the vector potential, which becomes perpendicular to the wire as the vector potential gets smaller away from it.
ihateblackbox
I am trying to understand how exactly electric and magnetic fields work.

So far this is my understanding. A particle which has charge has an electric field around it. If the charged particle moves, it forms a magnetic field with its force lines perpendicular to direction of the movement.

If this charged particle were an electron and it were to orbit a nucleus of an atom, then it would create a magnetic field perpendicular to the line between the electron and the nucleus. Now, in a normal piece of matter, there is not just one electron and there is not just one nucleus for those electrons so generally they tend to cancel out. Except for ferromagnetic materials where the electrons in orbit around different nuclei somehow line up to create a macro magnetic field. (I understand this is because these materials have partially filled outer shells which mean that due to Hund's rule, the electrons are more likely to have same spin direction. But I don't understand why materials above this proton number (still with partially filled shells) cannot have ferromagnetic property?).

If there's anything wrong there, please point out.

Moving on.

What I don't understand: when we apply a voltage across a conductor, the charged particles within it tend to move to the end which negates the voltage. OK, but why does this movement create a magnetic field which is CIRCULAR and not RADIALLY outward? Since the electrons are generally moving in 1 direction at a macro level, the magnetic field induced should be perpendicular to this direction in macro level. No?

This is obviously not true and I am trying to find out why it is not true. What am I missing?

A charged particle is not particle, it is a wave/particle. The moving charge particle/wave has a wave function. This wave function has a momentum associated with it. This momentum creates a momentum field called the vector potential field (Maxwell). The vector potential is in the same direction as the particle/wave velocity. This momentum field influences other charges near the moving particle. This influence is seen as the magnetic field. The magnetic field is defined as the Curl of the vector potential, and as the vector potential gets smaller away from the wire, the magnetic field appears perpendicular to the wire.

## 1. Why does a piece of wire have a circular magnetic field?

The circular magnetic field around a piece of wire is a result of the flow of electric current through the wire. As the current moves through the wire, it creates a magnetic field that is perpendicular to the direction of the current. This magnetic field forms a circular pattern around the wire due to the wire's cylindrical shape.

## 2. How does the current in a wire affect the shape of the magnetic field?

The strength and direction of the current in a wire determine the strength and shape of the magnetic field around the wire. A larger current will result in a stronger magnetic field, while a change in the direction of the current will result in a change in the direction of the magnetic field.

## 3. Can the shape of the magnetic field around a wire be changed?

Yes, the shape of the magnetic field around a wire can be changed by altering the direction or strength of the current flowing through the wire. Additionally, the shape can also be affected by the presence of other magnetic fields or materials in the surrounding area.

## 4. How far does the magnetic field extend around a piece of wire?

The magnetic field around a wire extends infinitely, but its strength decreases as you move further away from the wire. The exact distance of the magnetic field's reach depends on the strength of the current and the properties of the surrounding environment.

## 5. How does the magnetic field around a wire affect nearby objects?

The magnetic field around a wire can affect nearby objects by exerting a force on them. This is known as electromagnetic induction and is the principle behind many technologies, such as electric motors and generators. The strength of the magnetic field and the distance from the wire will determine the extent of this effect.

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