Making Lightning: The Van de Graaff Generator (page 2)

A hair-raising experience

1. Ground the conducting sphere.
2. Place an insulating surface on the floor near the van de Graaff generator. An inverted plastic crate works well for this purpose. The reason for doing this is to make sure no discharge occurs to conductors, such as water pipes, under the floor.



3. Place your hand on top of the generator with the palm of your hand face down.
4. Have someone turn on the generator. You can do it yourself, but be prepared for the possibility of a mild and harmless shock.
5. This works best with people with long, fine hair on low humidity days. If someone comes close, they could be mildly shocked.
6. When you are finished, turn off the van de Graaff generator, step off the crate, and discharge the conducting sphere.

Levitating pie pan

1. Ground the conducting sphere.
2. Place an aluminum pie tin on the conducting sphere.
3. Turn on the generator and observe the result.
4. Try this with several pie pans stacked on top of the conducting sphere.
5. Turn the generator off and ground the conducting sphere with the ground electrode to remove any residual charge.

Positive or negative?

1. Ground the conducting sphere.
2. Turn on the generator and bring the electroscope near the conducting sphere. Don't be totally surprised if you get a spark.
3. Rub the glass rod with the silk to produce a negative charge on the glass rod.
4. Bring the negatively charged glass rod to the top of the electroscope to separate the leaves.
5. Bring the negatively charged electroscope near the van de Graaff generator and observe whether the leaves separate further or move closer together.
6. Rub the rubber rod with the wool (or fur) to produce a positive charge on the glass rod.
7. Bring the positively charged rubber rod to the top of the electroscope to separate the leaves.
8. Bring the positively charged electroscope near the van de Graaff generator and observe whether the leaves separate further or move closer together.
9. Based on the response of the electroscope, what do you conclude about the type of charge produced on the conducting sphere of the van de Graaff generator?

Neon bulb

1. Turn on the van de Graaff generator.
2. Darken the room.
3. Bring a small neon bulb (with no electrical connections to either end) near the conducting sphere. If you get too close, some sparks will likely discharge harmlessly in your hand. If you prefer for this not to happen, you can rig up a nonconducting holder to support the neon bulb during this exercise. Be careful to avoid sudden moves that might result in dropping the bulb.
4. Position the neon bulb parallel to the floor on a line pointing toward the center of the conducting sphere. Move it closer and further from the van de Graaff and observe.



5. Position the neon bulb parallel to the floor on a line pointing perpendicular to the circumference of the conducting sphere, as shown in Figure 97-2. Move it closer and further from the van de Graaff and observe.
6. Turn the generator off and ground the conducting sphere with the ground electrode to remove any residual charge.

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