**Practice Problem on Electric Field for Point Charges**
Q1=+9 micro-C - o--------o Q2=+9 micro-C
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3cm | | |
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v | |
Q3=+7 micro-C - o--------o P4
|--2cm---|

3 charges are arranged on a rectangle as shown above.
What is the electric field at P_{4}?
Give the x and y components, the magnitude, and the direction.
Specify the electric field to three significant places
and the angle to the nearest integer.
Use the convention that right is 0 degrees, up is 90 degrees,
left is 180 degrees, and down is 270 degrees.

ANSWER = ( E_{x} = 1.92e+8 N/C, E_{y} = -1.42e+8 N/C, |E| = 2.38e+8 N/C, angle = 324 degrees )