What is the formula for magnetic field when v is close to c?

[IPhO' 2008]

We can use B = $$\frac{\mu}{4\pi}$$ $$\frac{q[vr]}{r³}$$
when v << c (c is a speed of light) but if v is nearly to c we can't use this formula.
What is a formula when v is nearly to c.

 

[IPhO' 2008]

r^{3[/SUP ] is r3}

 

[jtbell]

Is this supposed to be the magnetic field produced by a single moving charge? If yes, see

http://farside.ph.utexas.edu/teaching/em/lectures/node125.html

in particular equation (1539).

 

[IPhO' 2008]

Thank you.