How to Design a Charge Distribution for E Proportional to r^2?

[SirPencil]

Homework Statement

Design a charge distribution so that the resulting E is proportional to r^2.

The Attempt at a Solution

This is not really a homework problem just something our professor told us to think about at the end of our lecture. It made me really curious as to how you would do this.

You guys have any ideas or something to get me started?

Thanks

 

[gabbagabbahey]

Isn't there a Maxwell equation relating the electric field to the volume charge density that might help you here?