How Does a Positron's Kinetic Energy Change with Magnetic Field Strength?

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Homework Help Overview

The discussion revolves around the relationship between the kinetic energy of a positron and the strength of a magnetic field as it moves in a circular path of fixed radius. Participants explore how varying the magnetic field strength affects the kinetic energy while maintaining the same radius.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the equation relating charge, velocity, magnetic field, and radius, and how to derive a relationship between magnetic field strength and kinetic energy. There is an exploration of the proportionality of kinetic energy to magnetic field strength and the implications of velocity as a variable.

Discussion Status

Some participants have provided guidance on deriving expressions for velocity and kinetic energy, while others have acknowledged errors in their initial reasoning. There is an ongoing exploration of the mathematical relationships involved, with some participants suggesting that kinetic energy is proportional to the square of the magnetic field strength.

Contextual Notes

Participants are working under the constraints of a homework problem that requires them to maintain a constant radius while varying the magnetic field strength. There is an emphasis on understanding the relationships between the variables involved without arriving at a definitive solution.

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Homework Statement


A positron moves in a circular path of radius R due to a uniform magnetic field of strength B applied perpendicular to the plane of the circle. If B is varied, which of the following best represents a graph of the kinetic energy of the positron as a function of B so that the positron maintains the same radius R.

Homework Equations


qvB=mv^2/R

The Attempt at a Solution


KE = 1/2MV^2

Rearranging first equation, RqvB =mv^2, then multiply each side by 2

2RqvB = KE

Here i thought that KE is proportional to B, but v remains a variable that depends on KE. How do create a relationship between B and KE?
 
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Try using qvB=mv2/R to get an expression for v.
 
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Wow. I don't know how I messed that up. Graph is quadratic. Thanks for your help!
 
Good work.
 
2RqvB = KE

You could also note that v is proportional to KE^(1/2), and then since you don't need to worry about constants such as 1/2m you can just say that 2q KE^1/2 B is proportional to KE, and by dividing KE ^1/2 on both sides you get 2qB is proportional to KE^1/2.
so KE is proportional to B^2 and you get the answer that it is a quadratic formula centered at 0.
 

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