Van de graaff generator wonders

Details Activity Length 20-40 mins. Topics ElectricityForces & Motion Activity Type Discrepant Event (Demonstration only) Language English Print

Most people have seen a Van de Graaff generator before at a science centre or on TV. You know that it makes peoples" hair stvà on kết thúc, but bởi you actually know how it works?

Van de Graaff experiments are all based on the fact that lượt thích charges repel.

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A Van de Graaff generator pulls electrons from the Earth, moves them along a belt and stores them on the large sphere. These electrons repel each other và try to get as far away from each other as possible, spreading out on the surface of the sphere. The Earth has lots of room for electrons khổng lồ spread out upon, so electrons will take any available path baông xã to the ground.

The grounding rod is a smaller sphere, attached by a wire to lớn the Earth. It provides a convenient path for electrons lớn move to the ground. If we bring the grounding rod cđại bại enough khổng lồ the large sphere, the electrons rip through the air molecules in order to jump onto lớn the grounding rod, creating a spark và crackling noise.

When a fluorescent light tube approaches the negatively charged generator, the electrons on the generator flow through the tube and the person holding it. Flowing electrons result in an electrical current, lighting up the light tube. It doesn"t take very much current to lớn light a fluorescent bulb!

Putting Styrofoam peanuts or confetti on top of the Van de Graaff generator can create a cool trick. The electrons that collect on the sphere spread out into the Styrofoam peanuts and confetti, making the little, light objects negatively charged. When the negative charges on the peanuts repel the negative sầu charges on the generator, the peanuts push off the sphere.

When a student puts a hvà on the sphere, the electrons will spread out onto that person as they repel from the other electrons. They are most obvious in a person"s hair because the lượt thích charges of the electrons repel each other và cause the hairs to st& up and spread away from each other. As long as the person is standing on an insulated platkhung, the electrons will not be able to lớn travel down lớn the ground and their hair will remain standing up.

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Objectives

Explain how static charge causes materials to lớn attract or repel each other.

Materials

Key Questions

Where are the electrons? What is making your hair st& on end? Why doesn’t the hair come down after the machine has been turned off? What caused a shoông xã when the volunteer touched a fellow student? Why did your teacher ground the generator before allowing the volunteer to lớn step off the stool? What is the role of the plastic stool?

What To Do

Safety note: Make sure you ground the large sphere after each use by touching it with the ground wire or small sphere. Although the Van de Graaff generator produces a very low current, it may cause problems with people who have heart problems or a pacemaker. Warn students they may get small shocks which will scare them more than hurt them.

Part 1: Making Sparks

cảm ứng the small sphere (connected to lớn the ground wire) to lớn the dome.Turn the knob counter clockwise.Turn the generator on.Slowly turn the knob clockwise so the motor turns the belt.Take the small sphere away and let a charge accumulate on the dome. Ask a student to turn off the lights khổng lồ make it easier lớn see the sparks.Move the small sphere around the sphere in different positions so that everyone can see the sparks.

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Part 2: Sautéing Styrofoam 

Ground the dome by touching the grounding rod lớn it.Without removing the grounding rod, place Styrofoam peanuts (or confetti) on top of the large sphere.Take the ground away, and the Styrofoam peanuts will fly off the generator.This can be repeated by placing a metal pie panplate (or three!) on top of the generator and repeating the steps above sầu.

Part 3: Hair-Raising Experience

Ask a student lớn step up onto the insulated stool.Ground the dome by touching the grounding rod to it.Without removing the grounding rod, ask the volunteer to lớn put one hand on the dome, the other hand by their side và make sure they underst& not khổng lồ move their hands until you tell them lớn.Take the ground away, and their hair will start khổng lồ stand up. Shaking their head will help too!Hold the mirror so that the volunteer can see their new hair-do!Ask the volunteer to move sầu their h& from the ball to lớn their side, and to keep it there. Immediately ground the Van de Graaff& then turn it off.The volunteer can simply step off the stool or touch elbows with a classmate lớn get rid of their extra electrons (note: touching elbows will result in a shock!).

Extensions

Place a piece of giả fur on the large sphere, the individual fur strands will stvà. Tape streamers khổng lồ your volunteer, lượt thích an extra-long moustache! Have sầu someone hold onto lớn the large sphere while blowing soap bubbles with a wand, the bubbles will become positively charged và will be attracted to anything that is grounded e.g. a person walking by.

Chuyên mục: Kiến thức