Edexcel IGCSE Physics 复习笔记 2.4.4 Uses & Dangers of Static Electricity

• Electrostatic charges are used in everyday situations such as photocopiers and inkjet printers

Photocopiers

• Photocopiers use static electricity to copy paper documents, most commonly in black and white
• An image of the document is projected onto a positively charged copying plate
• The plate loses its charge in the light areas and keeps the positive charge in the dark areas (i.e the text)
• A negatively charged black toner powder is applied to the plate and sticks to the part where there is a positive charge
• The toner is then transferred onto a new black sheet of white paper
• The paper is heated to make sure the powder sticks (hence why photocopied paper feels warm)
  • The photocopy of the document is now made

   

• Inkjet printers work in a similar way, but instead of the black toner powder, a small jet of coloured ink is negatively charged and attracted to the correct place on the page

Insecticide Sprayers

• Insecticides are chemicals used to kill pests in order to protect crops
• In order to spray crops effectively whilst using a minimal amount of chemicals, the sprayer has to deliver the chemicals as a fine mist and cover a large area
• To achieve this, the insecticide is given an electrostatic charge (e.g. positive) as it leaves the sprayer
• The droplets of insecticide then repel each other since they are the same charge
  • This ensures that the spray remains fine and covers a large area

   

• They are also attracted to the negative charges on Earth, so they will fall quickly and are less likely to be blown away
• A similar technique is used in the spray painting of cars

• Static electricity can cause sparking
• There are various situations where static electricity can pose a hazard, for example:
  • The risk of electrocution (e.g from lightning)
  • The risk of a fire or explosion due to a spark close to a flammable gas or liquid

   

• There are dangers of sparking in everyday situations such as fuelling vehicles such as cars and planes
• Earthing is used to prevent the dangerous build-up of charge
  • This is done by connecting the vehicles to the Earth with a conductor

   

Fuelling Vehicles

• A build-up of static charge is a potential danger when refuelling aeroplanes
• Fuel runs through pipes at a fast rate
  • This fuel is very flammable

   

• The friction between the fuel (a liquid insulator) and the pipe causes the fuel to gain charge
• If this charge were to cause a spark, the fuel could ignite and cause an explosion

• This is prevented by the fuel tank being connected to the Earth with a copper wire called the bonding line during the refuelling
• The conductor earths the plane by carrying the charge through to the Earth which removes the risk of any sparks