# Homework Help: Moving Observer

1. Dec 2, 2009

### whatsapro

1. The problem statement, all variables and given/known data
Suppose E and B are measured by an ovserver at rest to be (in N/C)
E = [0,0,60] B = [0,0,0]

Now another observer travels close by in the +x direction at a constant speed of v = .8c with respect to the other observer.

A. What is E' be in the moving frame? DONE
b. what will B' be in the moving frame? DONE
c. If a charge q = 1micro C travels with the moving observer (v = .8c in the +x direction), what is the direction of F(em) according to the observer at rest?

d. what is the direction of F(em) according ot the observer moving along witht he charge?

2. Relevant equations

I assume F(em) = q[E + v/c X B] or the other ref frame version

3. The attempt at a solution

Which one do I use? If the observer is at rest, wouldn't he be seeing the v = .8 c ? That would not even matter cause B = 0 anyways right? I would still use F(em) = q[E + v/c X B] right?

for part D. I would use F'(em) = q[E' + v'/c X B'] where v' = ??? would it be 0 because they are traveling same v?

I understand that F(em) ne F'(em) but what is also confusing is that in both cases, the E field is the only contributing factor to the force. Is that assumption true?

2. Dec 3, 2009

### whatsapro

Am I missing something here? Its copied exactly how it is written on paper.