Electric Fields

[masamune]

1) In the first quadrant (x > 0, y > 0), the x-component of the net electric field is:

always positive.
always negative.
sometimes positive and sometimes negative.


2) In the third quadrant (x < 0, y < 0), the x-component of the net electric field is:

always positive.
always negative.
sometimes positive and sometimes negative.

For the first part, I explained that in the first quadrant, the x and y components of the field are both positive and so the net electric electric field will always be positive. Conversely, in the third quadrant, the x and y components of the field are always negative and so the net electric field will always be negative. Is my rationale correct? Refer to the attached pic btw if you have no clue what i'm talking about.

[Doc Al]

Get in the habit of stating the problem clearly. I'm guessing that the picture is meant to show a positive charge Q placed in what was a uniform electric field in the +x direction? And the problem refers to the net field?
For the first part, I explained that in the first quadrant, the x and y components of the field are both positive and so the net electric electric field will always be positive.
All they ask about is the x-component, so that's all you need consider. But, yes, both contributions to the net field are positive, so your answer is correct.
Conversely, in the third quadrant, the x and y components of the field are always negative and so the net electric field will always be negative. Is my rationale correct?
No. The uniform field has a positive x-component, but the field from the charge is negative. But the magnitude of the field from the charge varies with distance. Think it over again.

[masamune]

sorry about that doc. you assumed correctly though. thanks for your help