Figure: The Electric Force Field

In physics, a force field is a way to picture the effects that electric charges have on one another. Instead of talking about the force a positive (+) charge exerts on an electron, we can say the charge creates a force "field" in the empty space around it. An electron put down at any place in this force field is pulled towards the positive charge; a positive charge set down at the same place is pushed away.

Try putting down "test" electrons with the mouse to see which way the field points and how strong it is; the line points in the direction in which the electron will move, and the length of the line tells you the strength of the force at its current location. You can drag the mouse, or you can press the "R" key to have your computer put down electrons.

Credit: Physics 2000, Colorado University at Boulder, http://www.colorado.edu/physics/2000/index.pl.

http://www.colorado.edu/physics/2000/waves_particles/wavpart3.html