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## Homework Statement

Charges of 6µC are located at

*x*=0,

*y*= 2.0 m and at

*x*= 0,

*y*= -2.0 m. Charges

*Q*are located at

*x*= 4.0 m,

*y*= 2.0 m and at

*x*= 4.0 m,

*y*= -2.0 m. The electric field at

*x*= 0,

*y*= 0 is (11✕ 103 N/C) i. Determine

*Q*.

## Homework Equations

E=kq/(r

^{3})

## The Attempt at a Solution

E= kq/(r

^{3})(4m i + 2m j) + kq/(r

^{3})(4m i - 2m j)

E= kq/(r

^{3})(8m i)

E= kq(8m i)/((x

^{2}+y

^{2})

^{3/2})

Q= E((x

^{2}+y

^{2})

^{3/2})/k(8m)

Plug in all values and Q= 13.6 uC

The correct answer is -13.6 uC... At what point does the negative sign come in, and why?