changing kinetic E of charged particle in magnetic field -- Halbach array

[Fullperson]

hi, I read somewhere that you can't change a charged particle's (we'll say electron) kinetic energy with a strong magnetic field, that you only change the electron's direction. I'm assuming a frictionless environment. This is a silly question, I just wanted to make sure, thanks!

[berkeman]

To change its KE, you would have to do work on it, right? In what direction is the force on a moving charged particle due to a magnetic field? What cross-product equation describes this force? What about the cross product provides the answer to your question?

I'm moving this to the Homework Help forums, BTW, since it is coursework.

[Fullperson]

ok, you know about the free electron laser right? aka the wiggler? More precisely, I want to know if the particle accelerated through the halbach array slows slows down

[berkeman]

From the description of the array, it doesn't look like it would change the speed of the particle, but I don't know for sure. I'll move this to Advanced Physics and change the thread title to get some better views.

[Fullperson]

thanks!

[Final]

Hi...
If you change the direction of an electron (for example with a magnetic field) it generates radiation and so its kinetic energy changed (it slows down).

[berkeman]

Hi...
If you change the direction of an electron (for example with a magnetic field) it generates radiation and so its kinetic energy changed (it slows down).

Ah, good point. Like cyclotron radiation:

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