# Motion of a charged particle in a uniform magnetic field

1. Apr 2, 2012

### bobsmith76

See attachment.

I don't why a charged particle in a uniform magnetic field will move in a circle. Why can't it just continue straight in the direction its going until another force acts on it?

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2. Apr 2, 2012

### bobsmith76

ok, I'm starting to think that it's just a brute fact. that's just the way particles behave in a magnetic field and no explanation can be offered.

3. Apr 2, 2012

### tiny-tim

hi bobsmith76!

but that F force in your diagram is always sideways â€¦

if you believe the diagram, then how can the particle go straight when there's a sideways force on it?

4. Apr 2, 2012

### RobinSky

Think of it like this, the particle is feeling the force on the side, it makes it turn (but the velocity will not change). So now consider the same particle in a new point in the system, your particle has turned for a little bit, and now still feels the force on it's side, which will make it continue to turn.

Now do this for all following points that exist in it's path, and you will see it will continue to move in a circle.

As the diagram says, the force is always perpendicular to the direction it's moving.

Think of a centripetal force, if that makes it more easy.

5. Apr 2, 2012

### bobsmith76

ok, i get it now. thanks.