Electric charges moving and magnetic field

[haiha]

I know that a current creates a magnetic field and so do moving electric charges. My question is how fast a single charge moves so that it will create a magnetic field. Should its velocity be around c to make that?

Thks

 

[Meir Achuz]

A moving electron creates a magnetic field B~vXE/c.

 

[haiha]

Oh, cool, I can calculate the magnetic field of a current by this formula as well. Thanks.

 

[arunma]

This is the magnetic field generated by a moving electric charge.

$$\vec{B} =\frac{q \vec{v} \times \vec{r}}{r^3}$$

 

[griefchan]

I think that no matter how much of the charge are given, there should have a magnetic made. But whether or not it is easy to found .
is it ?

 

[kendr_pind]

to answer haiha's question, typically in an electrical ckt, the electrons don't move around with speed of light..infact surprisingly it moves with a drift velocity. this is typically around 1cm/sec ! yes, electrons' drift velocity is very slow...it is the velocity of the signal that moves with speeds comparable to light( well it depends upon the dielectric co-effs etc). "signal" here roughly means the electro-magnetic field through space...

 

[Meir Achuz]

I think that no matter how much of the charge are given, there should have a magnetic made. But whether or not it is easy to found .
is it ?

The magnetic field of a single moving charge is a tricky calculation using Special Relativity, especially if the charge is accelerating.