# Homework Help: Line charge in different frames.

1. Aug 21, 2009

### sludgethrower

Here is an interesting question (units are Gaussian):

An infinitely long strgiht wire of negligible corss-sectional area is at rest and has a uniform lineare charge density q_0 in the inertial fram K'. The frame K' (and the wire) move with a velocity v parallel to the direction of the wire with respect the the laboratory frame K.

(a) What are the electric and magnetic fields in the laboratory?

(b) What are the charge and current densities associated with the wire in the laboratory?

Relevant equations - Probably Lorentz Transforms, Maxwell Equations...

Solution Attempt - None

2. Aug 24, 2009

### gabbagabbahey

"None" is not an appropriate attempt at a solution.

As a hint, you might want to start by finding the electric and magnetic fields in frame $K'$.

3. Aug 26, 2009

### sludgethrower

That first comment gabbagabbahey is really very unhelpful. What is one to do if they can't even begin to tackle a question??? Surely that is is the best reason possible to ask for help! In future posts, would you prefer me to write down some wrong physics that I know is completely incorrect, just to satisfy you..?

Anyway I managed to solve this problem...

4. Aug 26, 2009

### Staff: Mentor

5. Aug 27, 2009

### sludgethrower

When I have worked out my own solution, I want to see if it is correct...the textbook I am using provides no solution. It is best to verify the plausibility of a solution if two people have done the problem independently. Even then, you can still learn even if both solutions are correct as the other person may have taken a different approach.

If the moderators of this board are going to be stubborn, and refuse to exhange their knowledge, then this is obviously not the site for me. I actually discovered this site through the brilliant site "mathlinks": the people that use the site are genarally pure mathematicians, rather than theoretical physicists. Would someone kindly refer me to a different site where people will happily share their wisdom?

6. Aug 28, 2009

### Staff: Mentor

If you are unwilling (or unable) to post the relevant equations and show your work on the homework/coursework problem, then yes, this is not the website for you. Best of luck.