# A plastic rod 1.9 m long is rubbed all over with wool

1. Sep 20, 2015

### TehFabled

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

A plastic rod 1.9 m long is rubbed all over with wool, and acquires a charge of -6e-08 coulombs. We choose the center of the rod to be the origin of our coordinate system, with the x-axis extending to the right, the y-axis extending up, and the z-axis out of the page. In order to calculate the electric field at location A = < 0.7, 0, 0 > m, we divide the rod into 8 pieces, and approximate each piece as a point charge located at the center of the piece.

2. Relevant equations

Pythagorean theorem

3. The attempt at a solution

A) Found the length of a single section of the rod to be .2375
B) length from the center to the center of section 2 to be <0,.594,0>
C) Charge on piece number 2 to be 7.5e-9
D) Approximating piece 2 as a point charge, what is the electric field at location A due only to piece 2?

This is where I got stuck
Found the unit vector to be (.762, .647, 0)
I plugged in my values to the point charge formula multiplied by the unit vector and got <-61.03,-51.823,0>
I don't know where I've gone wrong. Tried redoing the same steps in another version of the problem, and can't get the solution

2. Sep 25, 2015

### Greg Bernhardt

Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

3. Sep 25, 2015

### ehild

Check the sign of the components.
You have a sign error. And also some minor rounding errors.