# Static Electricity

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• Created by: mohap023
• Created on: 02-03-14 09:02

## Electrical Charges

A Van de Graaf generator can make your hair stand on end, it charges up because:

• The belt rubs against a felt pad and becomes charged
• The belt carries the charge onto an insulated metal dome
• Sparks are produced when the dome can no longer hold any more charge

Rubbing a polythene rod with a dry cloth transfers electrons to the surface atoms of the rod from the cloth, so the polythene rod becomes negatively charged.

Rubbing a perspex rod with a dry cloth transfers electrons from the surface atoms of the rod onto the cloth, so the perspex rod becomes positively charged.

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## Charges On The Move

The rate of flow of electrical charge is called the current.

• Insulators cannot conduct electricity because all the electrons are held in atoms.
• A conductor can only hold charge if it is insulated from the ground
• To charge an insulated conductor, it needs to be brought into contact with a charged object.

When an object is earthed, it is said to be discharged from conducting electricity.

If we supply a conductor with more and more charge, its electric potential energy increases.

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## Uses and Dangers of Static Electricity

The electrostatic paint sprayer:

• spray nozzle connected to positive terminal of electrostatic generator
• negative terminal is connected to the metal panel
• panel attracts paint droplets from spray
• droplets of paint pick up same charge and repel eachother, forming fine cloud of paint.

The electrostatic precipitator:

• it removes ash and dust from coal-fired power stations
• ash/dust particles pass through a grid of wires in precipitator
• Grid wires are negative so partices become negatively charged
• Charged particles are attracted onto positively charged metal plates
• Plates are shaken so ash and dust falls off and is removed.
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## Dangers of Static Electricity

Pipe Problems:

• petrol pipes must be earthed, otherwise it can become charged
• A build up of charge can cause a spark, or an explsion as fuel reacts with O2 in air
• Static electricity is also generated when grains of powder are pumped through pipes
• Friction between the grains and the pipe charges them.
• An explosion could happen due to a spark igniting the powder
• Doctors use anaesthetic gases  which are explosive during operations in hospitals
• If the gas escapes into air, a tiny spark could make it explode
• To eliminate this static charge, antistatic materials is used as floor surface
• This material is a poor electrical insulator so it conducts charge to Earth
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