Van de Graaff - urgent help please! (+rep)

Hi, can anyone give me a definitive answer of how a Van de Graaff generator makes your hair stand up when you charge it whilst touching it. Obviously the hair all takes on the same charge. But do you share the excess charge on the metal sphere (like a conductor would) or is it an induced charge kind of thing?

Thanks

Reply 1

bigmo7

17

http://science.howstuffworks.com/vdg1.htm

In science class you may have also done some experiments with static electricity. For example, if you rub a glass rod with a silk cloth or if you rub a piece of amber with wool, the glass and amber will develop a static charge that can attract small bits of paper or plastic.

To understand what is happening when your body or a glass rod develops a static charge, you need to think about the atoms that make up everything we can see. All matter is made up of atoms, which are themselves made up of charged particles. Atoms have a nucleus consisting of neutrons and protons. They also have a surrounding "shell" that is made up electrons.
Typically, matter is neutrally charged, meaning that the number of electrons and protons are the same. If an atom has more electrons than protons, it is negatively charged. If it has more protons than electrons, it is positively charged.

Some atoms hold on to their electrons more tightly than others do. How strongly matter holds on to its electrons determines its place in the triboelectric series. If a material is more apt to give up electrons when in contact with another material, it is more positive in the triboelectric series. If a material is more apt to "capture" electrons when in contact with another material, it is more negative in the triboelectric series.

Bit of reading but its explained well :smile:

Reply 2

kexy

16

paddyman4

Hi, can anyone give me a definitive answer of how a Van de Graaff generator makes your hair stand up when you charge it whilst touching it. Obviously the hair all takes on the same charge. But do you share the excess charge on the metal sphere (like a conductor would) or is it an induced charge kind of thing?

Thanks

http://tinyurl.com/md5kto

The excess charge then shows up on the outside surface of the container. Here, our container is the sphere. It is through this effect that the Van de Graaff generator is able to achieve its huge voltages. For the Van de Graaff generator, the belt is the charged object, delivering a continuous positive charge to the sphere.

http://science.howstuffworks.com/vdg4.htm

Reply 3

paddyman4

OP

14

Well thanks for replying guys but neither of you have mentioned hair at all. Just what static electricity is and how a Van de Graaff works.

Reply 4

Phugoid

Static electricity is when charged particles gather on the surface of some material. It's as simple as that. Electricity = charged particles (electrons), static = doesn't move.

When you touch a VdG, your hairs become negatively charged, and repel each other (like charges repel).

Your hairs can also stand on end when they become attracted to a positively charged surface. For example, when you rub a balloon on your head, negative charges gather on your hair, and positive charges gather on the balloon, so when they come into close contact, the charges attract each other.

You may be interested to know why it affects the hair and nothing else.

The triboelectric series is a list of materials in order of how easily they give up electrons when they come into contact with other materials. When a material gives up an electron (or gains them) it becomes charged. Materials like hair, nylon, etc, are at the top of this list. They give up their electrons very easily, and become charged very easily.

Reply 5

dave_chapman

You share the charge on the sphere, like any conductor touching it would. The reason you can do this is because the charge on the van de graaf is so large, and is constantly kept "topped up" by the belt. Then as all your hairs have the same charge, they repel each other.

Reply 6

Choccy94

9

The electrons are trying to escape because they are of the same charge and so are repelling. They go to places where they are more likely to be able to escape: Your hair.

Because your hairs all now have a like charge the hairs will all try to repel eachother so that's what causes them to spread out.

Van de Graaff - urgent help please! (+rep)

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