• Support PF! Buy your school textbooks, materials and every day products Here!

Calculating electric field at a point due to 2 charges

  • Thread starter mr_coffee
  • Start date
  • #1
1,629
1
Hello everyone, I'm just starting this problem and i'm already confused. I'm suppose to calculat the electric feild at the point P(x =3, y = 3) due to two charges, q1 = 4.0x10^-6C at the origin, and q2 = -3.0x10^-6C at x = 3.0m.

I'll try and draw the diagram.

....................................^ E1
.................................../
................................../
................................./
...............................(P)
................................|
................................|
................................v E2



(q1).........................(q2)



How did they know E2 will be point downard and E1 would be diagnoal like that? :bugeye: Thanks
 

Answers and Replies

  • #2
dextercioby
Science Advisor
Homework Helper
Insights Author
12,985
540
Decompose each vector in the two perpendicular components and add those 2 vectors using components.At the end,you'll have to use Pythagora's theorem to find the modulus,knowing the components.

Daniel.
 
  • #3
Doc Al
Mentor
44,910
1,169
The charge q2 is negative and directly below the point P; so the field E2 points straight down (towards q2).

Similarly, the field (E1) from q1, a positive charge, points away from q1 towards P, thus is at a diagonal. (What angle does it make with the x-axis?)
 
  • #4
I don't know, but you can just add the two electric fields together separately. The electric field at distance r is:

E(r) = Q/(4*pi*e0*r^2), where e0 is the permittivity of free space (8.854*10^-12).

At P, r from the charge q1 is 4.24 (root of 2*3^2), while r at P from q2 is 3. Calculate these two fields, add 'em together. Remember that the two fields aren't pointing in the same direction though - the y part of the field due to q1 can be added to the field due to q2, but not the x part.
 
  • #5
1,629
1
ahh i remember now! Sorry its been a year since i took this course and i forgot literally everything. It will make a 45 degree angle. I ended up getting the answer! thanks!
 

Related Threads on Calculating electric field at a point due to 2 charges

Replies
5
Views
1K
Replies
9
Views
3K
Replies
5
Views
3K
  • Last Post
Replies
1
Views
15K
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
1
Views
2K
Replies
6
Views
3K
Replies
14
Views
2K
  • Last Post
Replies
2
Views
824
Top