p4 foundation Physics

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  • Created by: keeleymay
  • Created on: 17-06-13 11:22
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  • P4
    • Electrostatics
      • An atom consists of a small positively charge nucleus surrounded by an equal number of negatively charged electrons.
      • In a stable neutral atom there are the same amount of positive and negative charges.
      • Electrostatic effects are due to the movement of electrons
      • Like charges REPEL, unlike charges ATTRACT
      • A dust precipitator removes all harmful particles from the chimneys/factories & power stations which pollute the atmosphere
        • 1- metal grid placed in the chimney and given a large charge from a high voltage supply
          • 2- Plates inside the chimney are earthed and gain opposite charge to the grid
            • 3- As dust particles pass through the grid they become the same charge
              • 4- Like charges REPEL so the dust particles are repelled away from the wires. They are attracted to the oppositely charged plates and stick to them.
                • 5- At intervals the plates are vibrated and dust falls off into collectors
      • paint spraying:  - the spray gun is charged
        • 2- all the particles become charged with the same charge
          • 3- like charges repel so spread out giving a fine spray
            • 4- object to be sprayed is given opposite charge to the paint gun
              • 5- paint is attracted to the frame due to opposites attracting
                • 6- the object gets an even coat with limited paint wasted.
      • Defibrillator :  procedure to restore regular heart rhythm, delivering an electric shock through the chest wall to the heart
        • 2 paddles are charged from a high voltage supply
          • placed firmily onto patients chest to ensure good electrical contact
            • electric charge is passed through the patient to make  their heart contract
              • great care is taken to ensure operator does not receive an electric shock
      • Variable resistor or rheostat changes the resistance
        • Thinner and longer wires have more resistance
        • Voltage(potential difference) is measured in volts using a voltmeter,    CONNECTED IN PARALLEL
        • For a fixed resistor as the voltage across it increases the current increases
          • For a fixed power supply as the resistance increased the current decreases
          • Resistance: voltage / current
            • Measured in ohms
    • Live, neutral and earth wires
      • The Live wire - carries the high voltage round the house
        • Neutral wire completes the circuit providing a return path for the current
          • The earth wire is connected to the case of an appliance to prevent it becoming live
            • A fuse contains wire which melts, breaking the circuit if the current becomes too large
              • No current can flow, preventing overheating and further damage to the appliance
      • Double insulated appliances do not need earth wires, as the outer case is not a conductor.
      • The rate at which an appliance transfers energy : power+ voltage X current
      • THE LIVE BROWN BEAR SITS ON THE EARTH GREEN AND YELLOW GRASS UNDER THE NEUTRAL BLUE SKY
    • Ultrasound  is a sound above 20 000Hz - a higher frequency than humans can hear
      • It travels as a pressure wave containing compression's and rarefactions
        • Compression's are regions of higher pressure and rarefaction's are regions of lower pressure
    • Longitudinal waves: Cant travel through a vacuum
      • The denser the medium the faster a sound wave travels
      • The higher the frequency or pitch the smaller the wave length
      • The louder the sound/powerful ultrasound, the more energy is carrued by the wave and the larger the amplitude
    • When ultrasound is used to breakdown kidney stones
      • high powered ultrasound beam is directed at tje kidney stones
        • The ultrasound energy breaks down the stones into smaller pieces
          • The tiny pieces are then extracted from the body in the normal way
    • Nuclear radiation causes ionisation by remvoing electrons from atoms or causing them to gain eelctrons
      • Radioactive decay is random process it inst possible to predict
      • Radioisotopes have unstable nuclei, they aren't held together strongly enough
      • The half life of an radioisotope is the average time taken for half the nuclei present to decay..
    • When alpha or beta particles are emitted from the nucleus of an atom the remaining nucleus is a different element.
    • Background radiation:  Radioactive substances present in rocks (granite and soil)
      • Cosmic rays from space
      • Man made sources radioactive waste from industry and hopsitals
      • Tracers: when using a tracer to locate a leak in a pipe also used in the body ;
        • Very small amount of gamma is put into the pipe
          • A detector is passed along the ground above the path of the pipe
            • An increase in activity is detected in the region of the leak and little or no activity is detected after this point
        • Smoke detector
          • Contains an isoptope which emits alpha particles
            • Without smoke the alpha particles ionsie the air which creates a tiny current that can be detected by the circuit in the smoke alarm
              • With smoke the alpha particles are partially so there is less ionisation of the air. The resulting change in current is detected so the alarm sounds.
          • Dating rocks: Granite contains traces of uranium- radioactive material
            • The uranium present in the rocks go through a series of decays, eventually forming a stable isotope of lead.
              • By comparing the amounts of uranium and lead present in rock its approx age can be found
    • Radiocarbon dating: Carbon 14 is a radioactive isotope that is present in ALL living things. By measuring the amount of it found in an archaeological find can measure its approx age.
    • Materials can be made radioactive: when their nuclei absorb extra neutrons in a nuclear reactor
      • X-rays and Gamma rays:
        • When x ray goes through the skin some of the body tissues absorb the ionisng radiation
          • Gamma rays and X rays have similar wavelengths but are produced in different ways
    • Trchnetium -99  is commonly used as a tracer as it only emits gamma
    • Fission occurs when  a large unstable nucleus is split up and energy is released as heat
      • The heat is used to boil water to produce steam... The pressure of the steam acting on the turbine blades makes it turn... The rotating turbine turns the generator producing electricity.
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        • FUSION: happens when 2 light nuclei fuse JOIN together- releasing large amounts of heat energy.
          • Needs- high temperatures difficult to achieve and manage on earth..
      • When uranium fissions a chain reaction starts, eg a nuclear bomb is an example of an uncontrolled chain reaction
  • An atom consists of a small positively charge nucleus surrounded by an equal number of negatively charged electrons.
  • high powered ultrasound beam is directed at tje kidney stones
    • The ultrasound energy breaks down the stones into smaller pieces
      • The tiny pieces are then extracted from the body in the normal way
  • Nuclear radiation causes ionisation by remvoing electrons from atoms or causing them to gain eelctrons
    • Radioactive decay is random process it inst possible to predict
    • Radioisotopes have unstable nuclei, they aren't held together strongly enough
    • The half life of an radioisotope is the average time taken for half the nuclei present to decay..

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