# Average electric field over a spherical surface

## Homework Statement:

Show that the average electric field over a spherical surface, due to charges outside the sphere, is the same as the field at the center.

## Relevant Equations:

This is where I'm stuck.
I'm sure the average is going to be an integral, but $\displaystyle\frac{1}{4\pi R^2}\oint\mathbf{E}\cdot d\mathbf{a}$ gives me a scalar, not a vector.