Disk and Electric Field's Direction

[Soaring Crane]

Homework Statement

A thin disk with a circular hole at its center, called an annulus, has inner radius R1 and outer radius R2. The disk has a uniform positive surface charge density omega on its surface.

Figure's link: http://i131.photobucket.com/albums/p289/SoaringCrane/yf_Figure_21_421.jpg

Find the direction of the electric field E. Consider points above the annulus in the figure.

Homework Equations

This part of the question is really conceptual.

The Attempt at a Solution

Since the disk's overall charge is positive, the force of a positive test charge above the annulus would be directed away from the hole. Therefore, the electric field's direction would be in the positive x-direction??

Thanks.

 

[Kurdt]

You are correct but can you show it using a vector diagram?

 

[m2003]

I would say that your reasoning is correct. The direction of the electric field at any point above the annulus would be away from the hole, in the positive x-direction. This is because the positive charge on the disk would repel any positive test charge placed above it, causing it to move away from the disk. The electric field is a vector quantity, meaning it has both magnitude and direction. In this case, the magnitude of the electric field would be dependent on the distance from the disk and the charge density, while the direction would always be away from the hole.