# Biot-Savart Law for a Point Charge

1. Jan 10, 2010

### discordplus

1. The problem statement, all variables and given/known data

Show that B for a point charge is equal to

2. Relevant equations

I'm not all that sure. I read that maxwell's equations can be used to derive this, so I'd imagine that it's

3. The attempt at a solution

If it were that, then, if i have a point charge moving at some constant speed along the x axis and I wanted to find B some distance R from it, at that point, I would create a circular path a distance x from the charge with radius R. I can find the electric flux due to the point charge throughout the entire circular disk. Because its moving with constant speed, i can find x(t) which is equal to vt setting my initial location for the charge at x = 0. Also because of the symmetry, B must be the same along the entire path since the charge is the same distance from every point on the path.

So, the flux as a function of the distance from the point charge is as shown in the picture below

http://img707.imageshack.us/img707/6956/itsazoo.png [Broken]

Now that equation really does NOT look like it's going to go anywhere productive so I want to ask if my concepts/setup are right before going any further.

Last edited by a moderator: May 4, 2017
2. Jan 12, 2010

### ideasrule

Keep going. Don't give up. Eventually, you will get the Biot-Savart Law.

(However, remember that you have to get rid of the cross product somehow. v cross r-unit is equal to vsin(theta) in magnitude, so substitute that to get rid of the vectors.)