# Thread: magnitude of field at center or rectangle.

1. ## magnitude of field at center or rectangle.

eletric field magnitude equation: E = F/|q0| or must i use: E k|q|/r^2 ?

The magnitude of each of the charges in the figure is 9.10 10^-12 C.

The lengths of the sides of the rectangle are 3.00 cm and 6.00 cm.

Find the magnitude of the electric field at the center of the rectangle in figures a and b.

here are the figures: http://img260.imageshack.us/img260/5163/37111607os9.png

The constant k is $\frac{1}{4\pi\varepsilon}$
I suppose you know the value of k. The only reason you can use $E=k\frac{q}{r^2}$ is because th charges are of the same value.
$E_2=E\angle arctg\frac{3}{1.5}$