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## Homework Statement

Three equal positive point charge of magnitude Q=7.00uC are located at three corners of a square of edge length d=4.8cm. A negative charge of -21.00uC is placed on the fourth corner.

A) At the position of the negative charge, what is the magnitude of the electric field due to the three positive charges?

B) What is the magnitude of the attractive force on the negative charge?

## Homework Equations

Ea=kQ/d^2 (also applies to Ec)

Eb=sqrt (Ea^2 + Ec^2)

e=KQ/r^2

r=sqrt(2d)

## The Attempt at a Solution

I haven't gotten to part B yet, but here is the work I have done for part A.

Ea=(8.99x10^9)(7x10^-6)/.048^2=2.7x10^7

Ec=2.7x10^7

Eb=sqrt(Ea^2+Ec^2)=3.86x10^7

The electric field at the negative point due to the corner charge: e=KQ/r^2

e=(8.99x10^9)(21x10^-6)/0.3098^2=1967053.444

Since e and Eb are parallel, to find the magnitude of the electric field you would need to add them together: e+Eb=4.1x10^7

I have no idea why this is wrong. I also tried breaking it down into vectors, but that also got a wrong answer as well. If that was the right line of thinking I can post the work for that, but it felt off to me. I am including the diagram I drew up a well. I only have one try left so any guidance to help me see what I am doing wrong would be greatly appreciated.