Physics Unit Four

Physics Unit Four

1. P4A - Sparks

   • Insulating materials
     • Metals = Good Conductors = electricity passes through them easily
     • Plastic = Shit Conductors
   • Positive and negative charges
     • Results between charges
       • Charges are the same = They Repel
       • One is charged and one isnt = They attract
       • Charges are different = They attract
     • Types of charges
       • Positively Charged (Loss of electrons) eg Acetate and Perspex
       • Negatively Charged (Gain of electrons) eg polyethene
   • Electrostatic Shocks
     • Friction made by synthetic materials becomes charged and causes a electrostatic shock
     • Problems with Static electricity
       • Dust and dirt is attracted to insulators like TV's and PC's
       • Dangerous when...
         • There are flammable gases or vapours or a high concentration of oxygen; can cause an explosion
         • You touch something with a large electric charge, making it flow through you body casuing an electric shock and possibly stop your heart
   • Safety Measures
     • Object that might become charged is earthed by an earth wire, so any charge immediately flows down the earth wire
     • Machinery operators stand on insulating mats or wear shoes with insulating soles.
     • Lorries containing flammable gases, liquids and powders are earthed by an earth wire before being unloaded.

2. P4B - Uses of electrostatics

   • Uses of static electricity
     • A paint/crop sprayer - Paint/insecticide droplets are charged, repel from each other and give a even coverage
       • Nozzle is positively charged and object is negatively charged
     • A photocopier and laser printer - uses charged particles to produce an image
     • A defibrillator - discharges heart, delivers a controlled electric shock through patients chest to try restart their heart
       • 1. Two insulated paddles are charged with a 300 - 1000 voltage 2. Conducting Gel is applied to patients chest before paddles are placed on chest 3. Electric charge is passed through to make the heart contract artificially
     • Electrostatic Dust Precipitators - Used to remove soot from smoke
       • 1. Smoke particles pick up a negative charge 2. Smoke particles are attracted to the collecting plates, which are earthed or positively charged 3. Collecting plates are knocked to remove the smoke particles, which then fall into a collector.
       • Metal grids in the electrostatic precipitator are given a high voltage

3. P4C - Safe Electricals

   • Electric Current - The flow of electric charge
   • Resistance (ohms) - used to limit the current and dim the light
     • Decreases in thin wire (less space for current to move)
     • Increases in thick wire (more space for current to move)
   • Cables and plugs
     • Comprises of two or three main inner wires, each with a copper core as an conductor and plastic outer layer as an insulator
       • Blue - Neutral - Completes the circuit Brown - Live - Carries the high voltage Green and yellow stripes - Earth - A safety wire to stop the appliance becoming live (cant be live whatsoever)
     • The Plug
       • bLue goes Left (Neutral)
       • bRown goes Right (Live)
       • sTripped goes Top (Earth)
     • Fuses - breaks the circuit if a fault in an appliance causes too much current flow
     • Circuit Breaker - resettable fuses that break the circuit if a fault occurs. They can be reset with the flick of a switch
     • Double Insulation - Appliance that doesn't need an earth connection as it has a plastic case

4. P4D - Ultrasound

   • Tranverse Waves - Right angle to the direction
   • Longitudinal waves - Parallel to the direction (Sound waves)
   • Wave Terms
     • Amplitude - The biggest distance the particles move from their normal position.
     • Wavelength - The distance between one compression and the next.
     • Frequency - The number of waves produced in one second, measured in hertz, Hz.
     • Compression - A region of higher pressure where particles are squashed together.
     • Rarefaction - A region of lower pressure where particles are spread out.
   • Term to given to sound thats higher than 20k Hz
   • Uses of Ultrasound
     • To break up kidney stones
     • To see soft tissue inside the body
     • To check for blood flow

5. P4E - What is Radioactivity?

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