# Magnetic field from free electrons

1. Oct 19, 2015

### Danyon

Does a beam of free electrons create a magnetic field like that of a wire with current flowing through?

2. Oct 19, 2015

### ZapperZ

Staff Emeritus
Yes. It is one way that we detect them when they pass through a section of a particle accelerator (i.e. using a device such as an ICT).

Zz.

3. Oct 19, 2015

### tech99

And could you say what shape the magnetic field of one travelling electro would take?
And could you tell me the shape of the magnetic field of one travelling electron please? Is it a spherical shape?

4. Oct 19, 2015

### Chandra Prayaga

That is a little more difficult to describe without using the equation for the magnetic field, but let me try. The field reduces with distance from the electron as 1/r^2. But there is also an angular dependence. For example, the field is zero directly in line with the velocity of the electron. If you draw any circle perpendicular to the velocity, with its center on the line of the velocity, the magnetic field is tangential to the circle at every point. So it is certainly not spherically symmetric. For that matter, even the electric field of a moving electron is not spherically symmetric.

5. Oct 19, 2015

### Staff: Mentor

A Google search for "magnetic field of a point charge with constant velocity" led me to a bunch of previous threads here on PF, including this post I made a few years ago:

Magnetic field of charge moving at constant velocity