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Electric Forces and fields question

  • #1
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
Incorrect. Your answer=B, Correct answer=D

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

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Answers and Replies

  • #2
BUMP!

There is the attachment for the diagram. :)
 
  • #3
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Don't forget the field lines are curved as shown by this diagram.

220px-VFPt_charges_plus_minus_thumb.svg.png


Now just imagine that diagram rotated to suit your question
 
  • #5
There I rotated it for you to make it easier to see.
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..
 
  • #7
Dick
Science Advisor
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Bump!
Figure the electric field at P due to B and the electric field at P due to A and add them as vectors.
 
  • #8
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
Figure the electric field at P due to B and the electric field at P due to A and add them as vectors.
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
Dick
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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?
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
How do I figure out the direction? The diagram arrows point towards in both ways?
 
  • #12
SammyS
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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
Incorrect. Your answer=B, Correct answer=D

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

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