Homework Help: Electric Forces and fields question

1. Jan 5, 2012

fatty005005

Two charges are placed at an equal distance x from point P, as shown in the following diagram. Charge A is placed directly west of P and B is placed directly north of P.

1)If A is given a charge of –Q and B is given a charge of +Q, what is the direction of the resulting electric field at point P?
A) southeast
B) northwest
C) northeast
D) southwest

I need an explanation on how it's done, especially on how you get the angle which it travels and stuff. Thanks

File size:
3 KB
Views:
95
2. Jan 5, 2012

fatty005005

BUMP!

There is the attachment for the diagram. :)

3. Jan 5, 2012

rollcast

Don't forget the field lines are curved as shown by this diagram.

Now just imagine that diagram rotated to suit your question

4. Jan 5, 2012

rollcast

There I rotated it for you to make it easier to see.

File size:
10.4 KB
Views:
93
5. Jan 5, 2012

fatty005005

Erm, I still don't see the connection? The + attracts the - charge, and i guess i have to use pythagorean theorem, but how do i calculate which direction it is deflected?

I need a explanation, i totally suck at this topic..

6. Jan 5, 2012

Bump!

7. Jan 5, 2012

Dick

Figure the electric field at P due to B and the electric field at P due to A and add them as vectors.

8. Jan 5, 2012

r4wr1m4d1n0

Well it's a repellent force from the north and an attractive force from the west, ergo, the added force vector is toward the southwest.

9. Jan 6, 2012

fatty005005

Erm, how do I go about the vector addition?

I have lEl= kQ/x^2 for the field of B and lEl=k(-Q)/x^2 for field of A. and shouldnt it be southeast? Why do you say it's southwest?

10. Jan 6, 2012

Dick

You are just giving the magnitude of the field. Electric fields have a direction. Those two fields have the same magnitude |kQ/x^2|. What's the direction of each of the vectors?

11. Jan 7, 2012

fatty005005

How do I figure out the direction? The diagram arrows point towards in both ways?

12. Jan 7, 2012

SammyS

Staff Emeritus
Forget the dipole diagrams !

What is the direction of the Electric Field at P due to the -Q charge at point A ?

What is the direction of the Electric Field at P due to the +Q charge at point B ?

How do the magnitude of these two fields compare?

Add the two fields vector-wise.