Sparks and Electrostatics

Charging Isolators, Electric Sparks, Uses of Electrostatics, Dangers of Electrostatics

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  • Created by: tom
  • Created on: 14-04-11 11:32

Charging Insulators

Rubbing can charge insulators like wool, plastic and rubber.

There two types of charges:

  •  Positive —
  • Negative —
  • Charged insulators can attract dust, fibres and small pieces of paper —
  • An insulator losing electrons will have a positive charge —
  • An insulator gaining electrons will have a negative charge —
  • Like charges repel and opposite charges attract —
  • A polythene rod rubbed with a duster acquires a negative charge and the duster acquires an equal but opposite positive charge —
  • The force between two charged objects are equal in size and act in opposite direction
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Electric Sparks

You will get an electrostatic shock when: 

  • You touch something that is charged
  • You become charged by walking on a carpet/vinyl floor and become earthed by touching a water pop or metal door handle —
  • Static charges are a nuisance as they cause synthetic clothes to ‘cling’ —
  • The transfer of charges between two objects creates an electric spark —
  • Electric sparks can generate high temperatures and therefore are dangerous near inflammable gases and vapours (e.g. Refuelling aircraft) —
  • The chance of receiving an electric shock can be reduced by correct earthing, using insulating mats or wearing shoes with insulating soles —
  • The risk of electric sparks can be reduced by securing a metal strap between the object and the ground —
  • The body acts as a good conductor of small amount of charge
  • An electric shock is safe through the body and long as it doesn’t go across the heart and cause a heart attack. If it goes through the hand down the leg it is unlikely to effect you but if it goes through one hand to the other hand as both are connected to earth
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Static Shocks Example

  •  The existence of repulsive forces between similar charges explains why you experience a shock if you touch an earthed conductor such as the screw on a light switch after walking across a synthetic carpet:
  • Synthetic carpets, for example those made of nylon, are good insulators
  • Charge builds up on the body when walking across the carpet due to the friction forces between shoes and the carpet
  • The similar charges repel each other but they cannot leave the body through the carpet which is a very good insulator
  • When the body is placed in electrical contact with the earth, electrons move between the body and the earth to discharge the body, creating a current which causes a shock
  • The direction of electron movement depends on whether the body is positively or negatively charged
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Uses of Electrostatics


  • Some uses of static electricity include:
  • Defibrillators
  • Photocopiers
  • Laser printers
  • Removing dust/soot from smoke chimneys
  • Spray painting
  • A defibrillator has two charged paddles. These are used to pass a charge through the patient to make the heart contract. The operator has to be careful not to be shocked. Good electrical contact is necessary between the patient and the paddles
  • Electrostatic dust precipitators are used in the chimneys of coal-burning power stations. They have metal plates/grids connected to high voltage. Dust particles are attracted to the plates/grids. When the dust particles are large enough, they fall down the chimneys
  • In spray painting the gun charged. The paint particles are repelled to produce a fine spray. The object to be painted is charged opposite to the paint. Attraction between the object and the paint ensures an even coat of paint. There is less waste in spray painting
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Dangers of Static Charge


  • Electrostatic charge is dangerous when it causes lightning and sparks that can ignite fuel
  • When an aircraft is being refuelled with kerosene (paraffin) and when a car is being refuelled with petrol friction forces cause charge separation
  • Charge separation result in the metal frame of an aircraft gaining an opposite charge to the fuel
  • This could result in a build-up of static charge on the metal frame of the aircraft or metal sleeve of the car refuelling pipe]if the voltage became high enough to cause a spark to earth, it could ignite the fuel
  • To prevent this, the framework of an aircraft is connected to earth before refuelling and the pipe leading to the petrol tank in a car is connected to the body of the car so that the charge can spread out, preventing the build-up of charge in a small area
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