Electric field along the axis of the disk:

$\overline{){{\mathbf{E}}}_{{\mathbf{x}}}{\mathbf{=}}{\mathbf{2}}{\mathbf{k\sigma \pi}}{\mathbf{(}}{\mathbf{1}}{\mathbf{-}}\frac{\mathbf{x}}{\sqrt{{\mathbf{x}}^{\mathbf{2}}\mathbf{+}{\mathbf{r}}^{\mathbf{2}}}}{\mathbf{)}}}$ where the x-axis points along the axis of the disk, r is the radius of the disk, k = 1/(4πε_{0}), and σ is surface charge density (Q/A).

Two 10-cm-diameter charged disks face each other, 30 cm apart. The left disk is charged to - 50nC and the right disk is charged to + 50 nC .

A)

What is the electric field E, both magnitude and direction, at the midpoint between the two disks?

Express your answer to two significant figures and include the appropriate units.

b)

What is the force F on a -1.4 nC charge placed at the midpoint?

Express your answer to two significant figures and include the appropriate units.

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