To add a charge distribution to the screen, select the appropriate object in the top menu in the right margin and double click where you want to add it. (E) means the object is oriented so that you see an end-view of the object and (S) means it is oriented so that you see a side view. You can select an object by clicking on it: the selected object is highlighted in green. Dragging the selected object will move it and pressing "Charge Up" (or typing '+') or "Charge Down" (or typing '-') will change its charge. The selected object can be deleted using the Delete button or the Delete key.

When you have arranged the objects as you wish, you can draw the equipotentials by pressing the Draw button, the return key, or typing 'd'. Areas with positive potentials have a red background while areas of negative potential have a blue background. Check the "Show potential" checkbox or type 'p' to get a readout of the potential at the cursor location. Check the "Show Field" checkbox or type 'f' to draw an electric field vector at the cursor location. Hold the shift key to multiply the arrow's length by a factor of 10. Adjust the contour step size slider to change the spacing of the equipotential curves.

Note that displayed potential values assume that the height of the display screen is 1 m and the charge unit is 1 nC. To rescale, note that displayed potential values should be adjusted in direct proportion to the charge unit and in inverse proportion to the screen height. For example, if a system is actually 0.1 m high or the unit charge is 10 nC instead of 1 nC, multiply the displayed value of the potential by a factor of 10.

This web app was written by Jake Hauser (Pomona '20) with tweaks by Tom Moore.