What is the Path and Speed of a Proton in a Magnetic Field?

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Homework Help Overview

The discussion revolves around the motion of a proton in a magnetic field, with specific parameters including velocity, electric field, and magnetic field strength. Participants are tasked with determining the path and speed of the proton as it exits the magnetic field region.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the implications of the Lorentz force on the proton's trajectory, questioning how the presence of both electric and magnetic fields affects its path. There are discussions about the shape of the path, with some suggesting it may be circular, while others consider the effects of the electric field on the motion.

Discussion Status

The conversation is ongoing, with participants sharing their attempts and seeking clarification on the interactions between the electric and magnetic fields. Some have proposed breaking down the problem into simpler cases to understand the combined effects, while others express uncertainty about the correctness of their approaches.

Contextual Notes

Participants note the complexity introduced by the presence of both electric and magnetic fields, leading to questions about the resulting trajectory and the need for potential integration to account for the proton's motion through the fields.

aldaris565
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Homework Statement



A proton travles with a velocity 8x10^5 m/s E=10^6 V/m and B= 1.5 T. Draw the path of the proton and what is speed of the proton when it comes out?

Here an image:

attachment.php?attachmentid=3457&d=1297476699.jpg


Homework Equations





The Attempt at a Solution

 
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As per PF rules, you need to show your own attempt before we can help you.

Please don't double post. Use this one, not the one in General Physics.
 
Yeah ok, I'm newbie in this forum... that's what i did :

[PLAIN]http://img222.imageshack.us/img222/3104/imagengh.jpg


But i don't know what else to do.. please help me =)
 
Last edited by a moderator:
OK, so you have the method, but where's your working?
 
Well just replace with the values given...I'm stuck i don't know if that's correct or not... I decided do it with all variables and then replace them...

I guess i sould integrate the speed getting the position (x,y) but I'm not sure if that's correct...

I need help.. I HAVE to resolve this problem...

I need ideas you don't have to resolve all the problem.. just give me ideas!
 
aldaris565 said:
Well just replace with the values given...I'm stuck i don't know if that's correct or not... I decided do it with all variables and then replace them...

I guess i sould integrate the speed getting the position (x,y) but I'm not sure if that's correct...

I need help.. I HAVE to resolve this problem...

I need ideas you don't have to resolve all the problem.. just give me ideas!

What is the shape of the path of a charged particle in a uniform magnetic field?

You correctly list the Lorentz force as the force that is acting on the proton in the magnetic field (there is no E field, right?). What does that Lorentz force do to the path of the proton? Draw the path, and plug in the numbers for the force. The force acts over a finite distance of the proton's trajectory -- what is the resulting trajectory when the proton leaves the B-field region?
 
berkeman said:
What is the shape of the path of a charged particle in a uniform magnetic field?

You correctly list the Lorentz force as the force that is acting on the proton in the magnetic field (there is no E field, right?). What does that Lorentz force do to the path of the proton? Draw the path, and plug in the numbers for the force. The force acts over a finite distance of the proton's trajectory -- what is the resulting trajectory when the proton leaves the B-field region?

But in the problem exist an E field... the trajectory doesn't have to be exact... i guess it's a Uniform Circular Movement.

If i'd do:

First for t=0 -> x=0 y=0.05
Then:
Finding t=? for x=0.3 y=0.05

That would be correct¿? then i replace that value of t in the formula of the speed... would i get the final speed (when it comes out) ??
 
aldaris565 said:
But in the problem exist an E field... the trajectory doesn't have to be exact... i guess it's a Uniform Circular Movement.

If i'd do:

First for t=0 -> x=0 y=0.05
Then:
Finding t=? for x=0.3 y=0.05

That would be correct¿? then i replace that value of t in the formula of the speed... would i get the final speed (when it comes out) ??

Ah yes, I missed that there is an E field too. So you have to use the full Lorentz force in the region between the plates, and account for the deflecting forces from the E and B fields.

If it were only the B-field, then yes, the particle would trace a circular path. Given the B-field direction shown, would the proton be deflected up or down by that B-field?

But you do need to add in the contribution of the E field as well. Which way will the E-field try to deflect the proton?

Since both the E and B fields are constant in the region between the plates, you should be able to just add their contributions. However, the bending path will make the proton stay between the plates a little longer than if it traveled in a straight line, so there may be an integration involved...
 
Maybe try solving separately for the E-field case and the B-field case, to see about what you can expect for the combined case, before doing any complicated integrals...
 
  • #10
The integrals are no so complicated... but in another forum someone told me that the proton never leaves and the path i guess it's not a straight line, because qE is diferent that q(vxB) [q(vxB) and qE are in opossite directions but they aren't equals to eliminate them...]
 
  • #11
aldaris565 said:
The integrals are no so complicated... but in another forum someone told me that the proton never leaves and the path i guess it's not a straight line, because qE is diferent that q(vxB) [q(vxB) and qE are in opossite directions but they aren't equals to eliminate them...]

What radius do you get for a B-field only version of this problem?
 

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