# Homework Help: Changing kinetic E of charged particle in magnetic field - Halbach array

1. Aug 15, 2008

### Fullperson

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

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!

2. Aug 15, 2008

### Staff: Mentor

Re: changing kinetic E of charged particle in magnetic field

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.

3. Aug 15, 2008

### Fullperson

Re: changing kinetic E of charged particle in magnetic field

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

4. Aug 15, 2008

### Staff: Mentor

Re: changing kinetic E of charged particle in magnetic field

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.

5. Aug 15, 2008

### Fullperson

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

thanks!

6. Aug 15, 2008

### Final

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

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).

7. Aug 15, 2008

### Staff: Mentor

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

Ah, good point. Like cyclotron radiation: