# Motors and magnetic fields

1. Jul 7, 2012

### crash_ndie

hello sorry for the bad description I've always loved physics since i was in school so Ive decided to start a project so please forgive my lack of technical wording and ignorance i promise am a quick learner lol

on a motor we use electricity / current passed though a coil to create a magnetic field focused down the center of the motor to make it spin.

My question is what happens to the field out side of the coil.

(wish could post a pic be so much easier to ask my question)

if the field in the center of the motor is , say 10 as its maximum what will it be on the out side of the coil ?

2. Jul 8, 2012

### Staff: Mentor

Hi crash_ndie. Welcome to Physics Forums.

I wouldn't exactly agree that the field is directed to the centre of the motor; the stator field is directed to where it will best interact with the rotor field.
I think you'll find in a typical motor that each pole is firmly bolted to the steel case of the motor, and poles alternate around the casing, N, S, N, S, and so on. So the magnetic lines of flux travel via the steel casing around to the adjacent poles to reenter the motor through the pole face of the adjacent poles. That way, very little flux strays beyond the motor.

3. Jul 8, 2012

### sankalpmittal

In a DC motor , when current flows in the coil, the magnetic field of coil interacts with the magnetic field of cylindrical field magnets , due to the combined effect , the coil is acted upon by a couple. The field is linked with the coil and another one is linked with cylindrical field magnets. At the centre of coil the effect of magnetic field is zero. They appear to be in same direction. Hence there are these two system of magnetic fields.

They are maintained constant. When coil plane comes at right angles to the plane of magnetic field of cylindrical magnets , the effect is zero but due to angular momentum it continue to rotate. After 180 degrees the split rings reverse and it continue its process like this, clockwise or anticlockwise.

4. Jul 8, 2012

### crash_ndie

say we base the motor on this type were the coil is out side and the rotor is in the center
see attatched pic..

on the second pic (best i could find to show the field) picture the magnet as the spining motor C & D.

on the field A, E & B whats happening to the field in relation to north and south, dose it flux n,s,n,s,n,s up the length of the coil to the center of the motor, Or is it a constant n,s to the center of the coil.

Basicly What am trying to find out, is the field as strong on the out side of a coil as it is in the center of the coil. Could this spare magnetic field be re - used

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