What Are the Effects of Five Charges in an Electrical Field?

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The discussion centers on calculating the electric field created by five charges in an electrical field, focusing on the contributions of each charge. The key points include determining the field at the center from a single charge and using symmetry to simplify calculations. It is established that the four middle charges cancel each other out, leaving the field direction influenced by the top charge. The participants clarify that since the top charge is positive, the field direction is downward, leading to the conclusion that option 4 is correct. The conversation emphasizes the importance of understanding both the magnitude and direction of the electric field in such problems.
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http://imgur.com/a3vxU


Really haven't a clue how to go about this, it's the last question on the paper and nothing before it is anything near as complex as this.

Any help much appreciated
 
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What's the field at the center from a single charge? Then find the vector sum of all the field contributions. Take advantage of symmetry.
 
Imagine the top charge is also absent. What would the field be due to the four charges?
 
So due to each charge the field is E=kq/r2

The 4 in the middle cancel, giving a field of either positive or negative of the single field charge above. So would the answer be option 3?
 
What is the direction of j? Of the field?
 
voko said:
What is the direction of j? Of the field?

The picture is all the info given on this
 
xma123 said:
So due to each charge the field is E=kq/r2
Good. That's the magnitude of the field, so be sure to count the direction.
The 4 in the middle cancel, giving a field of either positive or negative of the single field charge above.
Yes, the 4 in the middle cancel. But I don't know what you mean by "either positive or negative". Which is it? What's the direction of the field from the top charge?
 
You have enough information to deduce the direction of the field by the top charge. As for the direction of j, I am sure you have heard of the standard basis vectors i, j and k. What are they?
 
Apologies, it's late. The j vector acts in the y direction, so the top charge would act in the upwards of y, +j vector and therefore option 3.

By positive or negative I was referring to the difference betweent options 3 and 4.
 
  • #10
xma123 said:
the top charge would act in the upwards of y

Why is that?
 
  • #11
voko said:
Why is that?

Oh damn, they're positive charges, so the field acts downwards away from the top charge.

This would give a "negative" field in the y direction and so option 4 is correct?
 
  • #12
xma123 said:
they're positive charges, so the field acts downwards away from the top charge

Correct!
 
  • #13
voko said:
Correct!

Thanks very much for your patience, much appreciated
 

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