topic 11 - static electricity

• static electricity

  • electrons can transfer from one object to another when they are rubbed against eachother - electron transfer via friction
  • electrons can easily be lost as they are in the outer shells of an atom
  • in insulators electrons are not freely available to move but are generally static
  • when insulators are rubbed together , the friction causes electrons to leave one another and build up on another
  • the material that gains electrons will have a negative charge
  • material that lost electrons will have a positive charge
  • opposite charges attract
  • like charges repel
• • the electrons in the wall are repelled and move away ( like charges repel )
  • the positive charge left behind ( the induced charge ) attracts the negative charge on the balloon
• examples of static electricity

  • polythene - gains electrons from the cloth duster as there is now a negative charge on the rod of the same size
  • cellulose acetate - transfers electrons from the rod onto the cloth duster as the rod has a positive charge of the same time
• Friction with objects causes charge build-up on our bodies
• Contact with a conductor leads to electron repulsion and attraction to the conductor
• Electron flow towards the positive charge produces an electric shock or spark
• Similar phenomenon occurs in clouds due to friction between ice and water particles
• Built-up electricity in clouds can discharge to the ground as lightning
• Like charges repel, inducing charge transfer between objects
• This induces an opposite charge on the second object, leading to attraction
• Observable examples include bending a water stream towards a charged rod and picking up paper with a charged comb
• uses of static electricity - paint

  • the spray gun is charged positively which causes every paint particles to become positively charged
  • the same charge repel and the paint particles spread out
  • the object to be painted is give a negative charge and so attracts the paint particles
  • adv - less pain is wasted, the objects receives an even coat and the paint cover the awkward shadow surface that operator can see
• dangers of static electricity

  • large amount of heat produced in sparks
  • if spark occurs near something flammable can cause and explosion
  • places where flammable materials flow ( petrol stations) are particularly susceptible due to large amount of friction
  • prevented by earthing ( direct return path for electrons to the ground - called discharging ) objects
  • preventing any sparks
• danger of static electricity - air craft fueling - grounding

  • charges are able to flow through the metal wire to the ground and be discharged , preventing the build up of excess charge
  • as fuel flowing into tank creates friction , and transfer of electrons

  
• electric fields

  • a region of space in which a charge object experience a force
  • field lines represent the electric field around a single point or between two parallel plates
  • the higher density of electric field lines the stronger the attraction / repulsion

  A) radial fields

  B) uniform fields