- #1

LeeroyJenkins

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## Homework Statement

In free space, Q1 = 10nc at P1(0,-4,0) and Q2 = 20nC at P2(0,0,4).

a. Find E at the origin (answered)

E(r) = 5.617ay - 11.235az

b. Where should a 30nC point charge be located so E=0 at the origin? (need help)

## Homework Equations

E(r) = (1/4(pi)epsilon) sum ((Qm)am/(|r-rm|^2))

formula for electric field intensity

## The Attempt at a Solution

E = 0, Q3 = 30nC

E = 0 = (1/4(pi)epsilon) ( (Q1)a1/(|r-r1|^2))+ ...)

a3 = (0-x)ax + (0-y)ay + (0-z)az/ |r-r3|

x = 0

P3 = (0, y, z)

5.617ay - 11.235 az = ((Q3)a3/(|r-r3|^2))

*5.617ay - 11.235 az = Q3((0-y)ay + (0-z)az/ |r-r3|^3)

**|r-r3| = sqrt(0^2 + (0-y)^2 + (0-z)^2)

* and ** aren't enough to solve I'm missing one thing any help would be appreciated.

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