Explore electrical charges and static electricity using a Van de Graaff generator to demonstrate attraction, repulsion, and charge transfer.
To observe and understand electrical charges, static electricity, and the principles of charge transfer using a Van de Graaff generator.
A Van de Graaff generator is a device that creates static electricity and can generate very high voltages. It was invented by American physicist Robert J. Van de Graaff in 1929. The generator uses a moving belt to accumulate electric charge on a hollow metal sphere (the dome), creating a very high electric potential difference between the dome and ground.
The Van de Graaff generator consists of a belt running over two rollers, one at the bottom and one at the top inside a hollow metal dome. The bottom roller is typically made of a material that tends to give up electrons, while the top roller is made of a material that tends to accept electrons. As the belt moves, it carries positive charge up to the dome. The dome, being a conductor, allows the charge to spread over its outer surface, creating a high voltage.
Place the Van de Graaff generator on a dry, non-conductive surface. Ensure it is turned off before beginning setup.
Gather all materials and ensure everyone is wearing safety goggles. Make sure the area around the generator is clear of electronic devices and that the floor is dry.
Place the metal pie pan on top of the Van de Graaff generator dome. Turn on the generator and allow it to run for about 30 seconds. Place several small pieces of aluminum foil in the pan and observe what happens. Record your observations.
Turn off the generator. Tie a pith ball or Styrofoam ball to one end of the thread. Hold the other end of the thread and allow the ball to touch the dome of the generator. Turn on the generator briefly (5-10 seconds) and then turn it off. Observe what happens to the ball after it touches the dome. Record your observations.
If a volunteer is available and willing, have them stand on an insulating platform (like a plastic stool) and place their hand on the dome of the generator. Turn on the generator and observe what happens to their hair. Turn off the generator after 15-20 seconds or if the volunteer feels uncomfortable. Record observations.
Note: This step should only be performed with proper supervision and willing volunteers who do not have any electronic medical devices.
Place the electroscope (either from Experiment 11.2 or a commercial one) near the Van de Graaff generator but not touching it. Turn on the generator and observe what happens to the foil strips or needle of the electroscope as you move it closer to and further from the generator. Record your observations.
Turn on the generator and allow it to run for about 30 seconds. Carefully hold the fluorescent bulb near (but not touching) the dome. Observe what happens and record your observations.
Turn on the generator. Hold the metal pie pan by its edges with an insulating material (like a plastic ruler) and bring it near the dome without touching it. After a few seconds, touch the pan briefly with your finger while still holding it near the dome. Then move the pan away from the dome. The pan is now charged by induction. Test this by bringing it near small pieces of paper or the pith ball. Record your observations.
Turn off the generator and ensure it is fully discharged by touching the dome with a grounded metal object. Clean up all materials and return them to their proper storage locations.