STATIC ELECTRICITY

• Static electricity


  A property of all matter
• Positive and negative charges


  • If a body has the same amount of positive and negative charge, they cancel out, forming a neutral body (i.e. protons and electrons in a neutral atom)
• Like charges


  Repel
• Opposite charges


  Attract
• Insulators


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


  Can conduct electricity, their electrons can flow, and are not fixed (they are delocalised)
• Charging by friction


  1. Electrons are transferred from one object to the other

  2. Forming a positive charge on one object and a negative charge on the other
• If conductors were rubbed, electrons will flow in/out of them cancelling out any effect, so they stay neutral
• Insulators become charged because the electrons cannot flow
• A positive static charge forms on object which loses electrons
• A negative static charge forms on object which gains electrons
• Which object loses/gains electrons depends on the materials involved
• Sparking


  1. Charge builds up

  2. Objects are close but not touching

  3. Charge jumps through the air from the highly negative object to the highly positive object, to balance out the charges
• Lightning occurs when the charge difference between clouds and the Earth becomes so great, and a massive spark (lightning) jumps across to balance the charge
• Electrostatic force


  The force exerted on charged objects (of attraction/repulsion)
• Greater charge


  Greater force
• Closer together


  Greater force (force is proportional to the inverse square of the distance)
• Electrostatic force is a noncontact force, as force can be felt even when the objects are not touching
• Induction


  1. A positively charged balloon next to wall attracts electrons in the wall

  2. This causes the balloon to stick to the wall
• Comb charged

  Induces the opposite charge in small pieces of paper, so picks them up
• Earthing

  Allows electrons to flow to the earth, removing excess charge, allowing materials to stay neutral
• Applications of static electricity

  • Insecticide sprays are sprayed from aircraft, and given a charge
  • This means the spray droplets repel each other, so the droplets spread evenly, and are attracted to the earth
• If charge builds up and a spark forms when fuelling cars, it could ignite and cause a massive explosion
• Electric field

  • The region where an electric charge experiences a force
  • They point in the direction a positive charge would go (away from positive charges, and towards negative charges)
  • They point to charges at right angles to the surface
  • Stronger the charge, the more field lines present and the stronger the force felt
• Parallel plates have a uniform electric field