# Accelerating a stationary proton

1. May 30, 2010

### jeffreyl

1. The problem statement, all variables and given/known data

If you wanted to accelerate a stationary proton, would you use electric field or magnetic field? why?

2. Relevant equations

3. The attempt at a solution

2. May 30, 2010

### irycio

Oh, that's a nice question :D. Well, pretty simple actually. Just check and tell us, what does the force of each of the fields depend on? In this situation, one of them will be 0, and so this field will not accelerate a stationary proton.

3. May 30, 2010

### jeffreyl

actually that's the question. there's no other stuff. i think electric field would be used since magnetic field needs a existing velocity for a force to applied to the proton.

4. May 30, 2010

### irycio

So what's the problem, since you already know the answer and can properly justify it?:P

5. May 30, 2010

### jeffreyl

i have no idea if it's right or not. and my test is in a few days T_T

6. May 30, 2010

### irycio

Well of course it's right!
For electric field:
$$\vec{F}=q\vec{E}$$
$$\vec{a}=\frac{q \vec{E}}{m_p} \neq 0$$ under assumption that there is an electric field ;)

For magnetic field:
$$\vec{F}=q\vec{v}\vec{B}$$
$$\vec{a}=\frac{q\vec{v}\vec{B}}{m_p}=0$$, because v=0.

You could of course wirte it down more exactly, with all the angles considered and so on, but it doesn't change anything.

7. May 30, 2010

thanks :D