What Determines Electric Field Strengths of Two Charged Rods

[miyayeah]

Homework Statement

The problem I encountered goes like this: A 10cm long thin glass rod uniformly charged to 10nC and a 10cm long thin plastic rod uniformly charged to -10nC are placed side by side 4cm apart. What are the electric field strengths E1 to E3 at distances 1cm, 2cm, and 3cm from the glass rod along the line connecting the midpoints of the two rods?

Homework Equations

E= η/ε₀ = (4πK⋅Q) / A

The Attempt at a Solution

I am not quite confused about getting the answer to this problem but as to how I should approach the problem. I thought that the question was describing a capacitor, since the two rods are charged equally but oppositely. But when I tried to use the formula (as shown above), I realized I have no way to find the area. So, I realized that it was not a capacitor. How would I know, aside from looking at the formula, that the question is not describing a capacitor? Or when it describes a capacitor?

 

[kuruman]

To have a capacitor, you need two conductors near one another carrying equal and opposite charges. That's not what you have here because neither glass nor plastic can be considered as conductors. You need to find the electric field due to finite line of charge and superimpose the two fields.

 

[miyayeah]

To have a capacitor, you need two conductors near one another carrying equal and opposite charges. That's not what you have here because neither glass nor plastic can be considered as conductors. You need to find the electric field due to finite line of charge and superimpose the two fields.

Thank you for your explanation. Which formula should I use if I am solving for the electric field due to finite line of charge?

 

[kuruman]

Please read and understand this.
http://www.ece.k-state.edu//people/faculty/carpenter/documents/finite-line-field.pdf