What is the magnitude of the electric field (rod)?

[sunnnystrong]

Homework Statement

Two thin glass rods are placed side by side 4.70 cm apart as shown in the diagram below. They are each 11.3 cm long and are uniformly charged to +10.4 nC .

Answer the questions below regarding the electric field along a line which is drawn through the middle of the two glass rods (labeled Bisector in the diagram).

(Figure 1)

Homework Equations

*See attached file for relevant equations*

The Attempt at a Solution

Length = 0.113 m
λ = 9.20×10^−8 C/m
Eo = 8.85*10^-12
r1 = 0.037m
r2 = 0.01m

Using the attached equation... I got -1.21*10^5 N/C ... the magnitude of the field is 1.21*10^5 N/C

I know this is wrong but I am confused as to why?

 

[TSny]

Are you allowed to treat the rods as infinitely long?

 

[sunnnystrong]

Are you allowed to treat the rods as infinitely long?

Honestly, I have no idea. I am confused about how to set this problem up but found this equation in my book.

 

[sunnnystrong]

Are you allowed to treat the rods as infinitely long?

I would think not though as they gave you the length of the rods ?

 

[TSny]

I would think not though as they gave you the length of the rods ?

I tend to agree with you, that they do not want you to approximate the rods as infinitely long. But the formula for E that you are using is for an infinitely long rod.

Do you have an idea of how to handle the case of a rod of finite length? Are you using calculus in your course?