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"In theory, theory and practice are the same. In practice, they are not." ..."Albert Einstein (1879~1955, Mathematical physicist, Nobel Prize 1921-Physics)"

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 Author Topic: electron helical path simulation  (Read 9197 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
leeyiren
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 « Embed this message on: March 07, 2012, 07:06:13 pm »

hi, prof. would like to understand how electrons behave in a uniform magnetic field. why would they move in a helical path? any simulation? thanks
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Fu-Kwun Hwang
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 « Embed this message Reply #1 on: March 07, 2012, 08:08:04 pm » posted from:Taipei,T'ai-pei,Taiwan

If the initial velocity is zero then it will keep it that way.
If the initial velocity is in the same direction of the magnetic field, then the electron will move with constant velocity.
The force on the electron in the magnetic field is $\vec{F}=q\vec{v}\times\vec{B}$.
If the direction of $vec{v}$ is parallel to direction of $\vec{B}$, then $vec{F}=0$.
so it will move with constant velocity.

If the direction of $vec{v}$ is perpendicular to the magnetic field $\vec{B}$, then the force is also perpendicular to the velocity, so the force will only  change the direction of velocity -- and it is a circular motion.

If velocity contain both parallel component and normal component, it will move with helical path.

You are welcomed to check out Charged particle motion in E/B Field.
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"In theory, theory and practice are the same. In practice, they are not." ..."Albert Einstein (1879~1955, Mathematical physicist, Nobel Prize 1921-Physics)"