- #1

saintv

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**Determining Direction of Electric Field! :)**

## Homework Statement

Calculate the electric field at one corner of a square 50 cm on a side if the other three corners are occupied by 250 x 10^-7 C charges.

## Homework Equations

E = (kQ)/(r^2)

Where:

E = Electric Field Intensity in (N/C)

k = Electrostatics Constant (9 X 10^9 Nm^2/C^2)

Q = Charge in (C)

r = separation in (m)

## The Attempt at a Solution

Firstly, I calculated the E from one corner to each of the three charges:

E1 = [(9 x 10^9 Nm^2/C^2)(250 x 10^7 C)]/(.50m)^2

= 9 x 10^5 N/C (Not Sure of Direction)

E2 = [(9 x 10^9 Nm^2/C^2)(250 x 10^7 C)]/(.50m)^2

= 9 x 10^5 N/C (Not Sure of Direction)

E3 = [(9 x 10^9 Nm^2/C^2)(250 x 10^7 C)]/(.71m)^2

= 4.5 x 10^5 N/C (Not Sure of Direction)

(Note the change in r, as this is diagonal from the corner)

I then added the E.s up:

Etotal = E1 + E2 + E3

= (9 x 10^5 N/C) + (9 x 10^5 N/C) + (4.5 x 10^5 N/C)

Because E1 + E2 are not on the same plane, I would have to use Pythagoras to add the two, and then add it to E3. So,

Etotal = E1 + E2 + E3

= (9 x 10^5 N/C) + (9 x 10^5 N/C) + (4.5 x 10^5 N/C)

= (1.3 x 10^6 N/C) + (4.5 x 10^5 N/C)

= 1.8 X 10^6 N/C

Okay, wait. When I typed it out here and did all the calculations, I got the right answer! That's weird, considering every other time I did it it was wrong.

Anyway, I still have to determine the direction of the Electric Field.

In my answer key, it says: [AWAY FROM CENTER], which I do not understand. Is it because I am dealing with all positive charges, so they all repel each other?

I am simply terrible when it comes to determining direction, so please help!