# e field

by sasuke07
Tags: field
P: 54
1. The problem statement, all variables and given/known data
What is the magnitude of the collective contribution to the E field at the origin from both the + and - charges located 5 cm above the horizontal axis?

2. Relevant equations
kQ/d^2

3. The attempt at a solution
Im just having a problem setting up this problem. Could someone help me on getting started
Attached Files
 charges.pdf (8.2 KB, 2 views)
 PF Patron HW Helper Sci Advisor Thanks P: 25,496 hi sasuke07! (try using the X2 button just above the Reply box ) first, find the magnitude of each contribution, from that, find the x and y components … what do you get?
 P: 54 I already figured out the magnitued of the the positive charge 5 cm above the axis and got 5.4X10^4. What do you mean by the x and y components. WOuldn't the negative charge have the same magnitude of the positive charge.
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Thanks
P: 25,496

## e field

 Quote by sasuke07 WOuldn't the negative charge have the same magnitude of the positive charge.
yes
 What do you mean by the x and y components.
draw an arrow at the origin showing the direction of the field from the positive charge

then find the x and y components of that arrow

(and finally you'll add them to the x and y components of the arrow from the negative charge )
 P: 54 so to figure out the x component wouldn't it be Kq/d^2 where k=9X10^9, q is 30X10^9= charge and d would be .05m^2. Or would i have to use cosine and sine to figure out the x and y components and if so could you show me how to set it up.
 PF Patron HW Helper Sci Advisor Thanks P: 25,496 no, you must use cos and sin, of the angle the arrow makes
 P: 54 so would it be Kq/r^2sintheta and Kq/r^2Costheta. Where theta would be 90 degrees?
 P: 54 or would theta be 45
 PF Patron HW Helper Sci Advisor Thanks P: 25,496 θ is the angle of the line from the charge to the origin
 P: 54 awesome so 45 degrees.
 P: 54 So were the equations correct though?
 PF Patron HW Helper Sci Advisor Thanks P: 25,496 looks ok so what is the total field from both the positive and the negative charge?
 P: 54 i got 7.6X10^4 by doing KQ/r^2sin45 and the answer is the same for cos45. BUt i checked the answer and its supposed to be 7.1X10^4. Any suggestions
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