# Electric Field and an Uniformly Charge Plastic Pipe

A plastic pipe has an inner radius of a = 35.00 cm and an outer radius of b = 71.00 cm. Electric charge is uniformly distributed over the region a < r < b. The charge density in this region is 30.00 C/m3

A)Calculate the magnitude of the electric field at r = 0.44 m.

B)Calculate the magnitude of the electric field at r = 1.59 m.

I need some help on where to begin. I know the e-field for cylindrical sym. is E=2kQin/rL

I also know that Qin=charge density * Volume.

How do I find the volume so I can find the Qin in both A and B?

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siddharth
Homework Helper
Gold Member
Hint: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gaulaw.html" [Broken]

Have you figured out what gaussian surface to use? Once you do that, you'll be able to calculate the charge enclosed.

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I dont understand

siddharth
Homework Helper
Gold Member
What don't you understand?

I don't understand those formulas, we learned E=2kQin/rL. Was my approach the wrong way of doing it. Finding Qin and then using E=2kQin/rL to get the answer.

siddharth
Homework Helper
Gold Member
Yes, but more important than the formula is the underlying principle. Do you know how you got that formula?

Sorry to revive this old thread, but it is the exact same problem I am working on.

What is the formula used to solve the equation? I thought all I would have to do is E = lambda/2pi*epsilon*r^2 but I was wrong.

In the previous posts, in the equation E=2kQin/rL, what is L? Also, how do I find the volume so I can find the Qin in both A and B? Thank you.