Purpose: To compare the responses of objects with similar and dissimilar charges.
Summary: Students use a hand-crank Van de Graaff Generator to charge different objects to determine whether they attract or repel each other.
Question: Do objects with a similar charge attract or repel each other?
Method/Materials: Hand-crank Van de Graaff Generator, piece of Styrofoam packaging material, string, and glass rod.
Students should start by making sure the Van de Graaff generator is totally discharged by using the grounded discharge wand provided. Tie one end of the string around the Styrofoam ball (or packaging "peanut") and the other around the glass rod. Have each student determine what will happen to the ball when it comes in contact with the generator dome that has been charged. While one student turns the wheel to charge the dome of the generator, another student should hold the glass rod so that the ball is touching the dome.
After students have made their observations of what happens to the ball that comes into contact with the dome, allow them to make predictions of what will happen when the student holding the glass rod puts his hand near the ball. Will it be attracted or repulsed by the student's hand? Encourage students to discuss their predictions with their classmates and provide rationale for their prediction.
Students will note that the peanut will be repelled by the dome after a few seconds. Discuss what happened to the original charge on the ball and the subsequent charge from the dome. Why did they repel each other? Why was the ball attracted to the student's hand? Explain how electrostatics occurs when there is an exchange of charge on two or more different objects.
Hand-crank Van de Graaff Generator, piece of Styrofoam packaging material, string, and glass rod.