The electrophorus consists of a conductive (metal) electrode with an insulating handle and an insulating plate. Provision for grounding the electrode must be provided. First, the insulating plate is triboelectrically charged by rubbing it with a dry cloth. The resulting surface charge, while itself immobile, makes it possible to charge the electrode by induction. Click on the button below to begin.

Insulating Handle

Conductive Metal Electrode

Immobile Tribocharge on Surface

You can now move the electrode toward or away from the charged insulating plate by clicking once on the electrode and moving it with the mouse. You can stop moving the electrode by clicking on it again. Notice that the amount of induced charge separation increases as the spacing decreases, but the NET charge remains zero.

The electrode is now sitting atop the charged plate. The charge in the insulating plate is immobile. Click on the metal sparking ball and move it with the mouse to ground the electrode. Once the ball comes close enough, a spark jumps, the electric charge on the TOP surface of the electrode is conducted to ground, and the electric field above the electrode goes to zero.

The electrode is now at ground potential, but it also has net charge. Lift the electrode to its original position. Note that the charge, initially concentrated on the lower side of the electrode, distributes itself more uniformly on the top and bottom surfaces as the electrode is raised. Most importantly, the potential of the electrode rises dramatically.

With the electrode restored to its upper position, move the grounding ball toward it. A spark, longer than the previous spark because the potential of the electrode is higher, and more powerful because the capacitive energy has increased, now occurs to discharge the electrode. Note that it is electrons moving from ground along the wire that cancel out the positive charge of the electrode.

The electrode is now again at zero potential and the net charge is close to zero. Restart the interactive program to conduct the experiment again.