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# Resultant field Watch

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1. For this problem, shall I use cosine rule to work it out? Is it right?

2. (Original post by Daniel Atieh)
For this problem, shall I use cosine rule to work it out? Is it right?
The cosine rule is used to determine the lengths of sides of triangles, not a point. And those lengths are given. They are the distances to B.

I would rather regard the distances as a radius from a charge to the point B. If you have given the radius, you are able to calculate the electric field:

E = k*Q/r²

If you get the electrical field out, you can calculate the electrical field strength:

F = q * E = q * k*Q/r².*

That would be my way to determine the electrical field strength at B. I am not sure, if my considerations are right. ***
**
3. (Original post by Kallisto)
The cosine rule is used to determine the lengths of sides of triangles, not a point. And those lengths are given. They are the distances to B.

I would rather regard the distances as a radius from a charge to the point B. If you have given the radius, you are able to calculate the electric field:

E = k*Q/r²

If you get the electrical field out, you can calculate the electrical field strength:

F = q * E = q * k*Q/r².*

That would be my way to determine the electrical field strength at B. I am not sure, if my considerations are right. ***
**
Hi,

I hope that I misunderstand your posting. You mention that electric field strength as
F = q * E = q * k*Q/r².

I am interpreting that you are saying electric field strength is F. If this is really the case, I am afraid to say that you are wrong.

Electric field strength is F/q which is E.
4. (Original post by Eimmanuel)
Hi,

I hope that I misunderstand your posting. You mention that electric field strength as
F = q * E = q * k*Q/r².

I am interpreting that you are saying electric field strength is F. If this is really the case, I am afraid to say that you are wrong.

Electric field strength is F/q which is E.
Yeah, I have regarded the electrical field strength as F. Don't be afraid. I appreciate that you are correcting me. I am not perfect. Anything else what is wrong?
5. (Original post by Kallisto)
Yeah, I have regarded the electrical field strength as F. Don't be afraid. I appreciate that you are correcting me. I am not perfect. Anything else what is wrong?
Yes...

(Original post by Kallisto)
The cosine rule is used to determine the lengths of sides of triangles, not a point. And those lengths are given. They are the distances to B.
I think what Daniel had drawn were to represent the electric field vectors instead of the distances between the charges and point B.
So using cosine rule is perfectly good for this problem.
6. (Original post by Eimmanuel)
Yes...

I think what Daniel had drawn were to represent the electric field vectors instead of the distances between the charges and point B.
So using cosine rule is perfectly good for this problem.
Allright. So I have misunderstand the task completely. I thanked you that you have cleared the mistake. That was most kind of you.

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Updated: September 21, 2016
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