The links below are arranged roughly in order of increasing sophostication of the presentation. Some of the later ones are quite powerful and it may take a little longer to understand how they work.

A very simple display of field lines for 2 charges

Designed specifically to permit you to move the charge (on a line) and see the field change. This is slightly fancier than the example from uwstout.

Tutorial on Field lines As the name suggests, this applet is embedded in a tutorial. The particular advantage of this applet is that you can click a location to have the field line or equipotential line through that point drawn. The auto-drawn field lines are generally too dense here and appear to cross which is not permitted.

Moveable Test Charge

Four, Moveable Charges

Electric Potential Drag charges from the boxes and place them. Then check the "Show hi-res V" box. You will have to wait a little, but it will then show the potential on a fairly fine grid. It does not show equipotentials. If you place charges of opposite signs, note where the screen is white. This indicates V=0J/C. You can add charges and the applet will automatically redraw.

Field Lines and Equipotentials For me the labels on the check boxes don't show up. Checking the second one displays equipotentials. Checking the third one shows field lines. You insert charges by clicking on the main black area. The charge is set with the slider.

Sophisticated Electrostatics Applet Start by setting it to "Show E lines" in the third menu down. Try different charge configurations and then use the mouse to move charges around and see how that changes the field lines and equipotential surfaces (the white lines).

2D view of potential showing (by default) how positive charges would move. Try the point charge and dipole configurations first.

a 3D simulation Set it to show electric field lines first. Also try watching the behavior of the positive charges as they move around.

What happens to the electric field as a charge moves.

a pair of applets showing electric field and showing field lines with arrows and proper spacing

I'm classifying the links below as "games" but both do show interesting basic physics.

This one is a downloadable Java program so the link is to the page you download from. You want the one called Field Hockey. I got a file that said something about webstart and when I double-clicked on that, the applet ran. Field Hockey This doesn't show field lines or equipotentials, but does check your gut-level understanding of electric forces because you have to set charges to direct a hockey puck around obstacles to the goal.

This one is a downloadable Java program so the link is to the page you download from. You want the one called Field of Dreams. I got a file that said something about webstart and when I double-clicked on that, the applet ran. Field of Dreams This shows charged balls bouncing around in a closed box. It also shows the net electric field at all times and you can add an external field.