Understanding the Formula r=mv/Bq in Grade 12 Physics

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Discussion Overview

The discussion revolves around the origin and derivation of the formula r=mv/Bq, which relates to the motion of charged particles in a magnetic field. Participants explore concepts related to uniform circular motion and the forces acting on charged particles moving perpendicular to magnetic fields.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants inquire about the derivation of the formula r=mv/Bq and its relevance in grade 12 physics.
  • There is a discussion about the equation for uniform circular motion and the force on a charged particle, specifically F=qvBsin(theta).
  • Participants note that when the velocity and magnetic field are orthogonal, the force equation simplifies, leading to the relationship between magnetic force and centripetal force.
  • One participant describes a derivation process involving the relationships between force, mass, velocity, and angular velocity, concluding with the rearrangement to the formula r=mv/Bq.

Areas of Agreement / Disagreement

Participants generally agree on the simplifications of the force equations under specific conditions, but there is no explicit consensus on the derivation process or the origins of the formula r=mv/Bq itself.

Contextual Notes

The discussion includes assumptions about the conditions under which the equations apply, such as the orthogonality of velocity and magnetic field, but these assumptions are not fully explored or resolved.

mayodt
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Where did the formula r=mv/Bq come from in my answerbook for my grade 12 physics? Thanks.
 
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mayodt said:
Where did the formula r=mv/Bq come from in my answerbook for my grade 12 physics? Thanks.

Do you know the equation for uniform circular motion, given a force F that always points toward the center of the circular motion?

Do you know the equation for the force F on a charged particle q when it is traveling at velocity v perpendicular to a magnetic field B?
 
berkeman said:
Do you know the equation for uniform circular motion, given a force F that always points toward the center of the circular motion?

Do you know the equation for the force F on a charged particle q when it is traveling at velocity v perpendicular to a magnetic field B?

F=qvBsin(theta) is the equation right? and, I probably have seen the first one, but can't remember that specific one.
 
mayodt said:
F=qvBsin(theta) is the equation right?

Correct, but what does it simplify to when the velocity and B-field are orthogonal (at right angles to each other)?


mayodt said:
and, I probably have seen the first one, but can't remember that specific one.

See Uniform Circular Motion at wikipedia, and remember that F=ma:

http://en.wikipedia.org/wiki/Uniform_circular_motion

.
 
berkeman said:
Correct, but what does it simplify to when the velocity and B-field are orthogonal (at right angles to each other)?




See Uniform Circular Motion at wikipedia, and remember that F=ma:

http://en.wikipedia.org/wiki/Uniform_circular_motion

.

Ohh okay I got it. Because the force of the magnetic field equals the net force (F=ma) so that means that qvb=ma and then since v=rw and a=vw it's qrwB=mvw, and then the w's cancel out and you rearrange. Thanks a lot :biggrin:
 
mayodt said:
Ohh okay I got it. Because the force of the magnetic field equals the net force (F=ma) so that means that qvb=ma and then since v=rw and a=vw it's qrwB=mvw, and then the w's cancel out and you rearrange. Thanks a lot :biggrin:

Good job! :biggrin:
 

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