If a positive charge was... (1 Viewer)

[-X-]

If a stationary positive charge was sitting there doing nothing and suddenly a magnetic field was "turned on" over it. Will it experience any force? Im thinking it wont because it aint moving. But then again there is a relative movement between it and the MF for the split second and there is also a change in magnetic field in that split second. So which direction would the force be on the particle? Right hand rule doesn work for this (i think) so im thinking it doesnt move?

Heres a diagram showing what i mean:
Magnetic Field is turned Off:

Magnetic Field suddenly switched On, which way does it deflect?:

This isn't a question from an exam or anything, im just wondering if anything happens?


Thanks

 

[ND]

Good question, i dunno. I'd guess that the magnetic field's initial activation would affect it negligibly.

 

[-X-]

Ahh i think i got it now. The i described it is the equivalent of the positive charge moving Parallel with the magnetic field which means no force ie f = qvbsinTHETA and Sin 0 = 0.

 

[wogboy]

Good question!

The answer is no, there is no net force acting on the particle due to the magnetic field. All you are doing by switching on the magnetic field is that you're actually varying the magentic field intensity (B, in Teslas), however the particle itself is stationary with respect to the field (neither the field nor the particle is moving).

F = qvB, so if v=0, then F=0. Even if B changes with time, as long as v=0 then F=0.

It's not really because @=0 so sin@=0, because you cannot work out @ in this case (how do you know the direction of motion, for a particle which is not moving?

 

[ND]

Yeh ok but what if it was in the middle of a solenoid or something? Does the magnetic field start small and grow to its constant b or what? Laz? Wogboy? Anyone that knows?

edit: ah you answered my question before i asked it.

 

[-X-]

Originally posted by wogboy
All you are doing by switching on the magnetic field is that you're actually varying the magentic field intensity (B, in Teslas),

So when the magnetic field is "turned on" it isn't "moving" towards the south then? I thought that if the magnetic field was switched on, it would take some time to travel from the North to South.

 

[Dangar]

But doesn't there have to be some sort of motion with the magnetic field at the beginning even if it's miniscule? Just the action of the magnetic field kind of sweeping accross the floor as its set up if you know what i mean?? So then that would mean there would have to be some kind of force as the charge gets overwhelmed by the magnetic field

 

[SmokedSalmon]

I asked my father who is a physics professor and he states that nothing will hapen to the positive charge when a magnetic field is put onto it because it is not moving. So yeah

 

[wogboy]

So when the magnetic field is "turned on" it isn't "moving" towards the south then? I thought that if the magnetic field was switched on, it would take some time to travel from the North to South.

I think you must be confusing electric field lines with magnetic field lines. If you put a (initially stationary) positively charged particle into an electric field, there will be a force on it that pushes it in the direction of the electric field (i.e. towards the area of negative potential).

In a magnetic field, if the charged particle is stationary there is no force on it at all so it will stay stationary (i.e. not be attracted to the South pole). If however you move this particle inside the magnetic field (such that the angle of motion & the field lines are not parallel), only then there will be a force acting on it. In fact the particle will never be attracted towards the South pole (assuming a uniform magnetic field) due to the right hand rule (the direction of force is always perpendicular to the direction of the field).

 

[Dangar]

Originally posted by SmokedSalmon
I asked my father who is a physics professor

Im jealous!!! I want a physics professor in my house

 

[-X-]

Yeh i understand that now wogboy. Thanks Allot.

SmokedSalmon: Hey im jealous too what does your father do?

 

[SmokedSalmon]

Hehe of course u would be jealous!
My dad is a retired physics professor who used to teach at UTS. He is a great guy, helped me so much in comprehending physics. Would have understood nothing without him.

 

[MyLuv]

Errr...
Just a thought,in this case there's a change in magnetic field(switch on) thus it will produce an electric field(just like ElectroMagnetic Rad.) then this Electric field may interact with the charge in it??? Could it be???