# Electric field symmetry

Tags:
1. Dec 16, 2015

### Martin V.

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

In the attached figure, two curved plastic rods, one of charge q and the other of
charge q, form a circle of radius R 8.50 cm in an xy plane. The x axis passes
through both of the connecting points, and the charge is distributed uniformly on
both rods. If q 15.0 pC, what are the (a) magnitude and (b) direction (relative to
the positive direction of the x axis) of the electric field produced at P, the center of the circle?
2. Relevant equations
3. The attempt at a solution

My question:
Why is it that the electric field only have a component in the x-axis?

#### Attached Files:

• ###### spg.png
File size:
23.7 KB
Views:
52
2. Dec 16, 2015

### blue_leaf77

I think the question means the angle the net E field makes with the positive x axis (with the unit vector $\hat{x}$).

3. Dec 16, 2015

### J Hann

To get a better picture of the net field draw the electric field vector from a small segment of the curve
above the axis and the electric field vector from a corresponding segment below the x-axis

4. Dec 17, 2015

### Martin V.

Thanks #3 - with the drawing i found the reason :)