# Homework Help: Electric field between two charged rods

1. Oct 6, 2007

### aliaze1

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

Two 10-cm-long thin glass rods uniformly charged to are placed side by side, 4.0 cm apart. What are the electric field strengths at distances 1.0 cm, 2.0 cm, and 3.0 cm to the right of the rod on the left, along the line connecting the midpoints of the two rods?

2. Relevant equations

[1/(4??0)] * {|Q| / [r* (r2+(0.5L)2)0.5]}
the power "0.5" is the square root; √

3. The attempt at a solution

Calculating the charge @ 2cm seemed the easiest, so here is what I did:

L=0.1m
r=0.02m
Q=1*10-8
1/(4??0) = 9*109

plugging these numbers in, I get 83562.90218, and since there are two rods, and this is equidistant from both, I added Erod#1 + Erod#2, which is the same as doubling the value, giving 167125.8044; incorrect

2. Oct 6, 2007

### learningphysics

The two fields due to each rod are in opposite directions.

3. Oct 6, 2007

### aliaze1

so their signs are opposite....thanks!

4. Nov 16, 2009

### Logbert

This question is from section 27.3, Question 9 from the book "Physics for scientists and engineers second edition. A strategic approach" by Randall D. Knight, which is probably the most standard undergraduate physics text available and extremely good, and it even has answers for all the odd numbered questions.