# Homework Help: Determining directions of electric fields

1. Dec 12, 2013

### Coco12

How do you determine the direction of fields at the location o the source. if given that the charge is negative, the electrostatic force is away from the source . Do you reason that since the test charge is positive and the charge is negative, it will go towards the center?

2. Dec 12, 2013

3. Dec 12, 2013

### Coco12

Not really. Lets say if the electric field is pointing away from the center at a particular location. If a negative charge was placed at this location, what will be the direction of the electric force that it experiences?

4. Dec 12, 2013

Ah ok, for an electric field to be pointing away from a particular location there needs to be a charge there. If an another charge was simply placed on top of it, it would change the charge at that point, changing the field.

Last edited: Dec 12, 2013
5. Dec 12, 2013

### Coco12

So what would be the direction of the electrostatic force:
Do you judge on the negative charge and assuming that is a positive test charge, it will move towards the center?

6. Dec 12, 2013

It would be as it is in the point particle diagram. If there's an overall positive charge the field points away from the centre, if there is an overall negative charge it points in towards the centre.

Charge is defined to flow in the direction a positive charge would move.

7. Dec 12, 2013

### Coco12

So in my case, it would move towards the center right?

8. Dec 12, 2013

### Coco12

Also, can you see if you can answer my other question about electric potential difference?? Thank you!

9. Dec 13, 2013

You haven't said what size your charges are

10. Dec 13, 2013

### Coco12

Let's say there was an electric field pointing east with a magnitude of 1*10^2 n/c. A negative charge is placed at this location , what will be the direction of the electric force? It would be towards the center right since there is a negative charge?

11. Dec 13, 2013

I still find your phrasing very vague, I'm sorry.

I'd recommend drawing a diagram.

If I am reading you right then yes. All your field lines will begin pointing East. If a charge is thrown into the middle of that, the field lines will be drawn towards it.

12. Dec 13, 2013

### Coco12

This is the problem

13. Dec 13, 2013

I think it's against the rules of this forum for me to just give you the answer.

Do my previous answers make sense to you? Can you apply that to this question?

14. Dec 13, 2013

### Coco12

I think the way i have been doing it is right. What do u think? I don't need the answer, just whether my theory is right?