P4

P4

1. Sparks

   • Generating static electricity
     • insulated material can become electrically charged
       • when it is rubbed with another insulating matreial
       • the charge is called static electricity
         • transfer of electrons
           • electrons carry negative charges
           • leaving one object with a positive charge
           • new object has a negative charge
             • ion
   • Discharging electrons
     • an object can be discharged through earthing
       • the transfer of electrons from an object to the earth
         • can result in a electric shock
     • touching water pipes
       • friction cases water pipes to become negatively charged
         • this can cause a person to become charged if they have contact with the pipes
           • discharging results in a electric shock
   • Problems with static electricity
     • flour mills contain flammable atmospheres of fine particles
       • if there is a spark i can result in an explosion
     • lightning
     • dirt sticks to TV screens
     • fabrics stick to skin
   • Repulsion and Attraction
     • same charges will repel
       • perspex and perspex
     • oposite charges will attract
       • perspex and ebonite
   • Reducing danger
     • earthing
     • insulation
       • mats
       • shoes

2. Uses of Electrostatics

   • Everyday life
     • defibrillators
       • two charged paddles
       • discharges into patient
         • charge passes through patient to make the heart contract
     • chimneys
       • metal plates and grids are insulated in the chimney and connected to a high voltage, charging up dust that passes through the grids or plates
       • the dust particles are attracted to earthed plates, they form larger dust particle on contact
         • large particles fall back down the chemney
     • spraying
       • negatively charged paint gun
       • paint particals a negatively charge so they repel each other to get an even spray
       • positively charged panel is then sprayed
         • paint is attracted to the panel
   • Circuits
     • complete loop of electricity
   • fixed + variable resistor
     • fixed
       • longer wire
         • less current
       • thinner wire
         • less current
     • variable
       • rheostat
         • can change the length of the wire
   • Current, Voltage and Resistance
     • Resistance = Voltage / Current

3. Safe Electrical's

   • the 3 wires
     • Live
       • brown carries current
     • Neutral
       • completes circuit
     • Earth
       • earths the appliance
   • Fuse
     • circuit braker
       • switches a circuit off
     • fuse
       • breaks a circuit
   • how a fuse works
     • fuse wire gets hot
       • wire melts
         • circuit breaks
           • appliace is protected
   • choosing the right fuse
     • power =
       • voltage x current
   • earthing
     • 1) a fault causes casing to become live, due to a live wire touching it
       • 2) the circuit short circuits because the earth wire offers less resistance, large current
         • 3) fuse wire melts
           • 4) the circuit is broken
             • 5) the appliance is protected
   • double insulation
     • no earth wire

4. Ultrasound

   • Ultrasound
     • high frequency 20,000+ hertz
     • above humans hearing threshold
     • longitudinal wave
       • ampitude
         • wavelengh
           • frequency
   • applications of ultrasound
     • imaging
       • harmless
       • soft tissue
     • breaking down kidney stones

5. Radioactivity

   • Radioactivity
     • alpha emissions
       • two protons and two neutrons
       • particle differences
         • different element
           • atomic number decreased by 2
             • mass has decreased by 4
     • beta emissions
       • high energy electron
       • particle differences
         • different element
           • 1 more proton, 1 less neutron
             • atomic number is increased by 1
               • mass number remains the same
   • Half life
     • time it takes for half the undecided nuclei in a radioactive substance to decay. If the substance has a very long half-life then it remains active for a very long time