Field of five charges

  • Thread starter xma123
  • Start date
  • #1
9
0
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
 

Answers and Replies

  • #2
Doc Al
Mentor
45,010
1,286
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.
 
  • #3
6,054
391
Imagine the top charge is also absent. What would the field be due to the four charges?
 
  • #4
9
0
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?
 
  • #5
6,054
391
What is the direction of j? Of the field?
 
  • #6
9
0
What is the direction of j? Of the field?
The picture is all the info given on this
 
  • #7
Doc Al
Mentor
45,010
1,286
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?
 
  • #8
6,054
391
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?
 
  • #9
9
0
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
6,054
391
the top charge would act in the upwards of y
Why is that?
 
  • #11
9
0
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
6,054
391
they're positive charges, so the field acts downwards away from the top charge
Correct!
 
  • #13
9
0
Correct!
Thanks very much for your patience, much appreciated
 

Related Threads on Field of five charges

  • Last Post
Replies
2
Views
8K
  • Last Post
Replies
3
Views
8K
  • Last Post
Replies
8
Views
8K
  • Last Post
Replies
6
Views
5K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
3
Views
4K
  • Last Post
Replies
3
Views
9K
Replies
3
Views
17K
Replies
3
Views
592
Replies
4
Views
2K
Top