# Homework Help: Direction of magnetic field - moving charge

1. Apr 3, 2012

### jsmith613

1. The problem statement, all variables and given/known data
according to Maxwell a moving charge will create a magnetic field perpendicular to the direction of travel.
does this mean in ALL perpendicular planes (e.g: if the charge is moving to the left the magnetic field will act up, down, and side to side) or will it only act in one perpendicular plane. if it only acts in one plane then which plane will it act in?

Also why does this magnetic field not create a force upward / downward... on the moving particle
2. Relevant equations

3. The attempt at a solution
I could not post in the other section so have posed my question above.

Last edited: Apr 3, 2012
2. Apr 3, 2012

### tiny-tim

hi jsmith613!
the magnetic field is circular, it loops around the line of motion, see http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html for a pretty picture (and a thumbs-up)
suppose there was another particle moving parallel to the first …

the magnetic field would make it go in a circle, but would not cause it to change its distance (though the electric field would, of course) …

the original particle is at zero distance from itself, and that won't change, so no upward or downward force

(is there any spinning force? i can't answer that )

3. Apr 3, 2012

### jsmith613

here is another question:
if we had an EXTERNAL magnetic field, the magnetic force would be applied ppd to the direction of motion. would this cause centripetal acceleration?

4. Apr 3, 2012

### tiny-tim

a uniform magnetic field causes any charged particle to move with constant speed along a helix whose axis is parallel to the field

if the initial velocity is perpendicular to the field, then the helix becomes a circle (perpendicular to the field), and then yes the magnetic force will provide the centripetal acceleration