Charged particle in a magnetic field

[Tokspor]

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Which direction would the force be if a charged particle was moving parallel to a magnetic field?

 

[G1SG2]

Which direction would the force be if a charged particle was moving parallel to a magnetic field?

Magnetic Force Fb=qvb*sintheta. Think about it...

 

[neil100]

Come on folks. cross products. F= qv x B.

use the right hand fingers to decide.

middle: force
index: B
thumb: velocity, direction

if the particle is negative the force is in the opp. direction.

keep it simple. There are literally thousands of ways to ask a question related to this on the exam.

 

[Tokspor]

Nevermind that question. Not what I was getting at. I got a passage that said "if the velocity of a charged particle moving through a uniform magnetic field has a component parallel to that field the particle will move in a helical path as shown." And then they gave me a diagram that kind of looks like the left figure I drew below (my scanner doesn't feel like working today).

I thought we only considered the F and v values which are perpendicular to B. Wouldn't it move like this (the right figure)?

 

[G1SG2]

Come on folks. cross products. F= qv x B.

use the right hand fingers to decide.

middle: force
index: B
thumb: velocity, direction

if the particle is negative the force is in the opp. direction.

keep it simple. There are literally thousands of ways to ask a question related to this on the exam.

There is no force. The velocity is parallel to the magnetic field.

 

[neil100]

There is no force. The velocity is parallel to the magnetic field.

yes. i am talking about generally.

sine of 0 degrees or radians is 0.

 

[Tokspor]

Nevermind that question. Not what I was getting at. I got a passage that said "if the velocity of a charged particle moving through a uniform magnetic field has a component parallel to that field the particle will move in a helical path as shown." And then they gave me a diagram that kind of looks like the left figure I drew below (my scanner doesn't feel like working today).

I thought we only considered the F and v values which are perpendicular to B. Wouldn't it move like this (the right figure)?

Okay, I can see how the component of v which is parallel to the magnetic field will move the particle in the same direction as the magnetic field. But how is it possible that the circular motion caused by the force is suddenly perpendicular to magnetic field?

 

[neil100]

Nevermind that question. Not what I was getting at. I got a passage that said "if the velocity of a charged particle moving through a uniform magnetic field has a component parallel to that field the particle will move in a helical path as shown." And then they gave me a diagram that kind of looks like the left figure I drew below (my scanner doesn't feel like working today).

I thought we only considered the F and v values which are perpendicular to B. Wouldn't it move like this (the right figure)?

You didn't tell us the entire scenario.

What can get you that path is if you have a particle that has one velocity component parallel and another perpendicular to B.

there is no acc. since there is no force.
the only acc. contributed is by the velocity component perpendicular to B.
hence that helical path.

when you post always post the entire scenario. it's hard to answer questions and guess when you could have been more direct by writing two or three sentences of the actual passages. Idk people here don't get that.
But, I hope that helps.

 

[Tokspor]

You didn't tell us the entire scenario.

What can get you that path is if you have a particle that has one velocity component parallel and another perpendicular to B.

there is no acc. since there is no force.
the only acc. contributed is by the velocity component perpendicular to B.
hence that helical path.

when you post always post the entire scenario. it's hard to answer questions and guess when you could have been more direct by writing two or three sentences of the actual passages. Idk people here don't get that.
But, I hope that helps.

Thanks, that cleared things up. The passage did not say anything on which direction the velocity was. All they said regarding the figure was what I posted, plus the equation F=qvBsin(theta) and what the variables were. I just couldn't figure out why it was drawn as moving in such a way.

 

[thebillsfan]

this made me think of a question...if you have a charged particle that enters perpendicularly to a magnetic field, it experiences a force such that it starts traveling in a circle. when the velocity of the particle is in a direction tangent to the magnetic field, there should be NO more force. But the particle continues to travel in a circle--why?

edit: nvm that was a dumb question

 

[Tokspor]

this made me think of a question...if you have a charged particle that enters perpendicularly to a magnetic field, it experiences a force such that it starts traveling in a circle. when the velocity of the particle is in a direction tangent to the magnetic field, there should be NO more force. But the particle continues to travel in a circle--why?

edit: nvm that was a dumb question

If it's traveling parallel to the magnetic field, I don't think it would travel in a circle. However, if it is traveling even slightly askew from the magnetic field, there will be a component of its velocity which is in fact perpendicular to the magnetic field. This will cause the particle to travel in a helical motion (see the very first figure I attached). It won't be traveling in circles because there is that second component of its velocity vector which keeps it moving in another direction.