Like every Friday, the weekly "Physics Bite" column is back — number 15.
This time: the Van de Graaff generator, volts, and static electricity.
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The device in the video is called a **Van de Graaff generator**, and it uses mechanical motion to build an extremely high electrical voltage on the metal dome at its top.
When the girl in the photo touches the metal, electrons flow into her body, giving her a negative charge.
Because identical electric charges repel each other, her negatively charged hairs repel one another and "stand up."
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And for the curious — here's how it actually works:
Certain materials tend to release electrons (negatively charged) when they come into contact with other materials, while different types of material release protons (positively charged) instead.
The electrical voltage generated by contact between such materials is called static electricity.
Inside the generator's column, a belt made of insulating material rotates around two rollers (upper and lower), with small metal combs positioned near each one; the upper comb is connected to the metal dome.
As the belt spins and rubs against the rollers, the upper roller strips electrons from the belt and becomes negatively charged. Its high negative charge repels electrons from the nearby metal comb, pushing them up into the dome connected to it.
At the lower roller, the opposite process occurs — this roller is made of a material that strips protons from the belt, which in turn repels protons from the lower comb into a grounding conductor that carries them away.
As the belt keeps spinning, more and more electrons are deposited onto the metal dome, and the electrical voltage builds up to thousands or even millions of volts.
For comparison — an ordinary battery delivers 1.5 volts.
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It's important to remember that such a high voltage is not necessarily dangerous.
A volt is the measure of the force with which electric current is pushed out of a material, and it arises from the difference between a positively charged material and the negatively charged material toward which the electricity flows.
An ampere, by contrast, defines the quantity of electrons flowing through a conductor at any given moment, and a watt defines the total power over a given period of time.
The danger of electric shock depends on the amount of current flowing through the body — so a low current is not dangerous even if the voltage is high.
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Generators like these were once used to produce X-rays and to accelerate subatomic particles in particle accelerators.
More advanced technologies have since been developed, and the use of these generators has declined.
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