Presenting .. your Equipotentials!

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Note : when the lines are red -
the applet is calculating the electric field .. wait a second for it to finish.

Introduction : This applet illustrates the connection between the Electric field lines (or vectors) and the Voltage Equipotentials for different charge configurations. The default view is the Electric field lines. Try the charge configurations below, and then switch to the different views available.

Charge configurations:
Single positive charge     Single negative charge
Two equal positive charges    Two equal negative charges
Equal unlike charges    Unequal like charges
Unequal unlike charges

Also, the charges are "dragable"! You can click down on a charge and move it around (it will have to recalculate the electric field lines though - be patient!).

We could now look at a "vector field" illustrating the same idea. The benefit is that we can illustrate the strength of the field (with color) as well as the direction, and it is much faster (since we pick some discrete points and calculate the electric field at that point - rather than trying to plot a complete continuous trajectory of the line). Click the radio button below for the Electric field vectors. Notice that the color indicates the strength - and the individual vectors show the direction of the field at that point. [Pick one configuration and flip between the two views - they should look similar, in terms of the directions.]

            Electric field lines           Electric field vectors
            Equipotentials only       E vectors & Equipotentials
            Equipotentials and Electric Field Lines      

Things to try :
     With the vectors - move one charge on top of another!
     With unequal unlike charges and vectors - can you find the E=0 point?

Extra feature .. animation! If you put the test charge somewhere in the system, you can click the RESTART/PLAY button to "release" the test charge from rest - it will be acted upon by the other charges and move toward or away, depending on the net force on the test charge (if it hits one of the charges, there will be a "collision" and the animation will stop). Now, using that RESTART/PLAY button will start the test charge from rest! If you want to pause the motion, and not move the charge, then continue that same motion, use the RESUME FROM PAUSE button. [See, I found that if you move the charge to a new place, you want to start it from rest .. otherwise the applet would keep the old velocity from the pause - which caused weird, non-physical behavior. So, if you move the charge - use the RESTART/PLAY button ... if you just pause the motion, and then want to continue that motion without you adjusting the test charge .. use the RESUME FROM PAUSE.]

Hey, my charge disappeared! If you test charge flies off the screen to either side, or if it collides with one of the fixed charges - use the RESET button to restore the initial configuration.

Adding Equipotential lines at certain places :Assuming you have the equipotential lines showing, you can add your own line, just by double-clicking at the location you choose - the applet will figure out which equipotential line fits that point, and will draw it .. you can use this technique to "fill in" lines in different places (or to look for the V=0 line between two unlike charges!). [Unfortunately, if you then move the charges, the "old" lines that you added stay where they are - that's a quirk of the physlet, and I haven't been able to work around it. You would have to "reselect" that configuration from the choices in the upper right part of the screen to clear out the old lines.


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