Static Electricity

• Charges which are not free to move
• Build up of static is caused by friction
• 1. When certain insulating materials are rubbed together, negatively charged electrons will rub off from one of them and transfer to the other
  2. Both materials will be electrically charged with positive static charge on and an eqaul negative static charge on the other
  3. The way that the electrons are transferred depends on the material
  4. The polythene and acetate rods being rubbed with a cloth duster.
• Electrons move from the duster onto the rod

  
• Electrons move from the rod onto the duster

  
• The electrons from the jumper transfer onto the balloon.

  The balloon gains a negative static charge, whilst the balloon gains a positive static charge.

  The balloon is attracted to the jumper because the positively charged particles (protons) attract the negatively charged particles (electrons)

  Initially both objects had a neutral charge
• Only electrons can move
• In conducting materials, the charged electrons would flow away
• When a charged plastic rod is rubbed against a duster:

  • The electrons transfer from the rod onto the duster, so the rod gains a positive charge whilst the duster gains a negative charge
  • The electrons transfer from the duster onto the rod, so the duster gains a positive charge, and the rod gains a negative charge.

  We are able to attract small pieces of tissue paper to the rod, regardless of its charge
• A negatively charged rod repels the electrons on the neutral tissue paper, leaving more protons near the surface, meaning that the paper is attracted to the rod
• A positively charged rod attracts the electrons on the neutral tissue paper, the electrostatic force attracts the paper
• The material that loses electrons is left with an equal positive charge
• Too much static charge causes sparks or shocks:

  1. As electric charge builds on an object, the potential difference between the object and the earth increases (starts at 0V)
  2. If the potential difference gets large enough, the electrons can jump across the gap between the charged object and the earth, causing a spark.
  3. These electrons can jump to any earthed conductor nearby; this is how you can get static shocks from a car. A charge builds up on the car's metal frame; when you touch this, the charge through you to earth
  4. This happens when the gap is small, not a big one (like lightning)
• Like charges = repulsion

  Opposite charges = attraction

  • Two electrically charged objects will exert a force on each other.
  • These forces are stronger when close but weaker when further away
  • Electrostatic force is a non-contact force (not touching), will cause the object to move if they can
  • When an object becomes charged by being rubbed against another object, the objects will have equal and opposite charges
• Van-Der-Graaf generator

  • produces positively charged Particles
  • The voltage is high but the current is low
  • builds a static charge, when the rubber belt driven by a motor transfers to the dome
• Uses:

  • photocopiers
  • laser printers
  • electrostatic precipitator = removing smoke from factory emissions
  • paint sprayers = painting