Static Electricity

• Static electricity


  The build up of electrical charge within or on the surface of an insulated object
• If something has the same amount of positive and negative charge, the charges cancel out forming a neutral object
• Like charges


  Repel
• Opposite charges


  Attract
• Insulators


  Do not conduct electricity because their electrons cannot flow throughout the material, they are fixed
• Conductors


  Can conduct electricity, the electrons are delocalised
• Charging by friction


  When two insulators are rubbed together, electrons are transferred from one object to the other, forming a positive charge on one object and a negative charge on the other
• If two conductors are rubbed, electrons will flow in or out of them cancelling out any effect, so it remains neutral
• Insulators become charged because the electrons cannot flow
• Positive static charge


  Forms on an object which loses electrons
• Negative static charge


  Forms on an object which gains electrons
• Sparking


  1. Occurs when enough charge builds up, and the objects are close but not touching

  2. The spark: when a charge jumps through the air from the very negative object to the very positive object, to balance the charges
• Lightning


  Occurs when the charge difference between clouds and the Earth becomes so great, and a massive spark jumps across to balance the charge
• Electrostatic force


  The force experienced by charged objects
• Greater charge


  Greater force
• Objects closer together


  Greater force
• Electrostatic forces


  Noncontact forces as it can be felt even when the objects aren't touching
• Earthing


  Allows electrons to flow to the earth, removing excess charge, allowing materials to stay neutral
• Insecticide spraying


  1. Spray droplets are given a charge

  2. Droplets repel each other

  3. Droplets spread evenly

  4. Droplets are attracted to the earth

  5. If not charged there is a risk that some droplets will blow away or the spray will fall unevenly
• Preventing sparks when fuelling cars

  1. As fuel passes through the hose to the vehicle a static charge can build up

  2. When the charge is too large a spark might form

  3. The resulting spark might ignite the fuel

  4. Hoses are earthed to stop this occurring
• Electric field


  • The region where an electric charge experiences a force
  • They point in the direction a positive charge would go, away from positive and towards negative
  • They point to charges at right angles to the surface
• Stronger charge


  More field lines present and the stronger the force felt
• Parallel plates


  Have a uniform electric field