# Magnetic field around wire

• v_pino
In summary, a magnetic field can be created by a wire with current flowing, regardless of the presence of force or motion. This is due to Ampere's Law, which states that the magnetic field is directly proportional to the current enclosed by a surface. The magnetic field also depends on the distance from the current.
v_pino
Why will there be a magnetic field going around a wire that has current flowing?

I thought we need current and force perpendicular to each other in order to have a magnetic field. In a wire with current flowing, we don't have a force (motion).

Yes there will be a magnetic field. You do not need any force to create a magnetic field.

For example a charge moving at a constant velocity will produce a magnetic field, even though the net force on the charge must be zero.

This all follows from Ampere's Law, which, for magnetostatics, is:

$$\oint \vec{B} \cdot d\vec{l} = \mu_o I_{enc}$$

In words this says that, the magnetic field going around an arbitrary path times the "perimeter" of that surface is equal to a constant times the current enclosed by the surface. So, the magnetic field only depends on the current, or moving charge, plus how far you are away from the current (contained in the perimeter term).

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The presence of a magnetic field around a wire with current flowing is a result of the interaction between the moving charges (electrons) in the wire and the magnetic field they create. When a current flows through a wire, the electrons are in motion, creating a magnetic field around the wire. This magnetic field is perpendicular to the direction of the current flow and follows the right-hand rule, where the fingers point in the direction of the current and the thumb points in the direction of the magnetic field.

According to the laws of electromagnetism, whenever there is a flow of electric charge, there will be a magnetic field associated with it. In the case of a wire with current flowing, the moving electrons create a circular magnetic field around the wire. This magnetic field is essential for the functioning of many electronic devices, such as motors and generators.

It is important to note that the force and motion you mentioned are not the only factors that can create a magnetic field. In the case of a wire with current flowing, the motion of the electrons is enough to produce a magnetic field. This is because electrons have a property called spin, which is a type of angular momentum that also contributes to the creation of a magnetic field.

In summary, the magnetic field around a wire with current flowing is a result of the interaction between the moving charges (electrons) and their spin. This phenomenon is a fundamental principle in electromagnetism and plays a crucial role in many technological applications.

## 1. What is a magnetic field?

A magnetic field is a region of space where a magnetic force can be detected. It is created by moving electric charges.

## 2. How is a magnetic field around a wire formed?

A magnetic field around a wire is formed when an electric current flows through the wire. The moving electrons in the current create a circular magnetic field around the wire.

## 3. How does the direction of the current affect the magnetic field?

The direction of the current determines the direction of the magnetic field. The right-hand rule can be used to determine the direction - if you point your thumb in the direction of the current, your fingers will curl in the direction of the magnetic field.

## 4. What factors affect the strength of the magnetic field around a wire?

The strength of the magnetic field around a wire depends on the magnitude of the current, the distance from the wire, and the material of the wire. Increasing the current or decreasing the distance from the wire will result in a stronger magnetic field.

## 5. How is the magnetic field around a wire measured?

The magnetic field around a wire can be measured using a magnetic field sensor, such as a magnetometer. The strength of the magnetic field is typically measured in units of tesla (T) or gauss (G).

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