Physics P2 Topic 1

Physics P2 Topic 1

1. Static Electricity

   • Uses and dangers
     • Uses
       • Insecticide spraying
         • Nozzle of sprayer connected to electricity supply
           • Droplets get same kind of static charge
             • Droplets repel each other and the spray is spread out
       • Paint sprayers
         • Nozzle of sprayer connected to electricity supply
           • Droplets get the same kind of charge so they spread out
             • The object being painted given opposite charge
               • The paint is attracted to the object so less paint is wasted
     • Shocks and earthing
       • You can build a charge of static electricity
         • You may feel a shock when touching metal items
           • This happens as electrons move to cancel out the charge on you
             • It is called Earthing
               • Electrons flow through you to the earth
               • Lightning happens when charge of static electricity builds in clouds
                 • When charge grows big enough charged particles flow through air
                   • The energy released causes light and sound
                     • Lightning can damage or kill living things and destroy buildings
             • You will now be discharged
         • When walking across a carpet or sitting on a chair
   • Electrostatic charges
     • Electrons transferred from one material to another
       • Insulating materials can be given an electrostatic by rubbing two materials together
     • Material that has gained electrons has negative charge
       • Materials that lose electrons have positive charge
         • Equal charge size as negative material
   • Atoms
     • Nucleus containing protons and neutrons
       • Electrons move around nucleus
     • Atoms have same number of protons and electrons
       • + and - are balanced so no charge
   • Charging by induction
     • A charged object can attract uncharged objects
       • Happens because charged object induces a charge in the uncharged object
       • Balloon has negative charge
         • Electrons in wall are repelled and positive charge is left which attracts balloon
           • Protons cannot move

2. Electric currents

   • Direct current
     • An electrical current in a wire is flow of electrons
     • Current supplied by cells and batterys
       • This is direct current (d.c.)
         • Electrons flow in same direction
           • Electrons pushed out of one end of cell and flow around to other end, must be a complete current
   • Charge and current
     • Size of current is measure of how much charge flows past a point each second
       • It is rate of flow of charged particles

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