This simulation shows the electric field for up to three point charges in 3-D. The point charges can be moved by dragging. Click once to move a point in the xy-plane, and click a second time to move a point along the z-axis. Charges can be adjusted using the sliders. Set the charge to zero to hide the point. The display can be zoomed and rotated using the mouse or a touch screen.

[list=1][*]Can you make the electric field be zero at one or more locations without setting all of the charges to zero?[/*][*]Does the field for two negative charges look the same as for two positive charges? If not, what changes?[/*][*]What does the electric field look like if you put the three charges very close to each other?[/*][/list]