P4: Radiation for Life

Sparks
1. Electrons: Negatively charged, contained in atoms and surround positively charged nucleus, equal number to protons.
  1. Same amount of + and - charges in a stable, neutral atom
    1. The movement of electrons cause all electrostatic effects.
      1. The law of electric charge: like charges repel, unlike charges attract
        When a polythene rod is rubbed with a duster, electrons are transferred from the duster to the polythene, so the rod gets - charge
        When acetate rod rubbed with duster, electrons are transferred from the acetate to the duster, leaving the rod with a + charge
        An object will have a - charge with an excess of electrons, and a + charge with a lack of electrons
        Ions: atoms that have become positively or negatively charged
2. Electrostatic Shocks
  1. When inflammable gases or vapours are present, or there is a high concentration of oxygen, a spark from static electricity could ignite the gases or vapours and cause an explosion
    1. If you touch something at high voltage, lots of electric charge could flow through your body to earth. Even a small amount of charge could be fatal
      1. Static electricity can be a nuisance but isn't fatal. Dust and dirt are attracted to insulators like TV screens. Clothes made from synthetic materials can cling to the body and each other
        If an object that could become charged is connected to earth, any charge build-up will flow straight away down that earth wire
        Avoiding electric shocks
        In a factory where machines could become charged, the user stands on an insulating mat so the charge can't flow to earth
        If workers are at risk of charge building up, they wear shoes with insulated soles so it can't flow through them to earth
        Fuel tankers are connected to aircraft by a conducting cable during refuelling
        Anti-static sprays, liquids and cloths made from conducting materials carry away electric charge to prevent it building up
Uses of Electrostatics
1. Dust Precipitator: removes harmful particles form the chimneys of factories and power stations that pollute the atomsphere
  1. A metal grid/wires is placed in chimney and given a large charge from a high voltage supply
    1. Plates on chimney inside are earthed and gain the opposite charge to the grid
      1. As dust particles pass close to the grid, they gain the same charge as it
        Like charges repel, so the dust particles are repelled from the grid. They are attracted to the oppositely charged plates, sticking to them
        The plates are vibrated at intervals and dust falls down to a collector. They gain/lose electrons to become charged
        The charge on the dust particles induces a charge on the earthed metal plate. Opposite charges attract so the dust is attracted to the plate
2. Paint Spraying: Uses static electricity
  1. Spray gun is charged, all paint particles gain same charge, like charges repel so particles spread out to give fine spray, object to be painted given opposite charge to paint, paint attracted to object as opposite objects attract and paint sticks, object gets an even coat and waste limited
    1. If object not charged, paint moves onto it but it becomes charged from paint so they have same charge, and further paint is repelled from object
      1. Therefore object given opposite charge to paint. If paint has - charge having gained electrons, object should have + charge having lost electrons
3. Defibrillators: defibrillation is a procedure to restore a regular heart rhythm by delivering an electric shock through the chest wall to the heart
  1. 2 paddles are charged from a high-voltage supply, they are placed on the patient's chest firmly to ensure good electrical conduct, electric charge is passed through the patient to make their heart contract, and care is taken to make sure the operator doesn't receive and electric shock
    1. If a defibrillator is switched on for 5 milliseconds (0.005 s), the power can be calculated from: power = energy/time = 400/0.005 = 80000 W
Safe Electricals
1. Resistance: a variable resistor/rheostat changes the resistance. Longer lengths of wire have more resistance; thinner wires have more resistance
  1. Voltage (potential difference) is measured in volts (V) 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 increases, the current decreases.
    1. Formula for resistance: resistance = voltage/current, R = V/I
      1. Resistance is measured in ohms
        Resistance formula can be rearranged to find out: voltage = IR or Current I = V/R
2. Live, Neutral and Earth Wires
  1. Live wire carries high voltage around the house
    1. Neutral wire completes the circuit, providing a return path for the current
      1. Earth wire is connected to the case of an appliance to prevent it becoming live
  2. A fuse contains wire which melts and breaks the circuit if the current grows too large. Then no current can flow, preventing overheating and further damage to the appliance
    1. Earth wires + fuses stop a person receiving an electric shock if they touch a faulty appliance. As soon as the case becomes 'live', a large current flows in the earth and live wires and the fuse 'blows'
      1. A re-settable fuse (circuit-breaker) doesn't need to be replaced to restore power; it can be re-set
3. Electrical Power
  1. The rate at which an appliance transfers energy is its power rating: power = voltage x current
    1. The formula for electrical power can be used to calculate the correct fuse to use in an electrical device e.g.: power = voltage x current, current = power/voltage, mains voltage = 230 V, power of kettle = 2500 W, current = 2500/230 = 10.9 A. Therefore a 13A fuse is required
Ultrasound
1. Longitudinal Waves
  1. Ultrasound: sound above 20000 Hz, a higher frequency than humans can hear. It travels as a pressure wave containing compressions and rarefactions
    1. Compressions are regions of higher pressure and rarefactions are regions of lower pressure
      1. Features of longitudinal sound waves
        Can't travel through a vacuum. The denser the medium, the faster a sound wave travels
        The higher the frequency or pitch, the smaller the wavelength
        The louder the sound, or the more powerful the ultrasound, the more energy is carried by the wave and the larger its amplitude
      2. In a longitudinal wave the vibrations of the particles are parallel to the direction of the wave
        In a transverse wave the vibrations of the particles are at right angles to the direction of the wave
2. Uses of Ultrasound
  1. When used to break down kidney stones: a high-powered ultrasound beam is directed at the kidney stones, the ultrasound energy breaks the stones down into smaller pieces, and the tiny pieces are then excreted from the body in the normal way
    1. When ultrasound is used in a body scan, a pulse of ultrasound is sent into the body. At each boundary between different tissues some ultrasound is reflected and the rest is transmitted. The returning echoes are recorded and used to build up an image of the internal structure
      1. Reasons Ultrasound can be used for body scans
        When it is reflected from different interfaces in the body, the depth of each structure is calculated by using the formula distance = speed x time, knowing the speed of ultrasound for different tissue types and the time for the echo to return
        The proportion of ultrasound reflected at each interface depends on the densities of each of the adjoining tissues and the speed of sound in the adjoining tissues
        If the tissues are very different (e.g. blood and bone) most of the ultrasound is reflected, leaving little to penetrate further into the body
        The information gained is used to produce an image of the part of the body scanned
      2. Ultrasound is preferred to x-rays because it can produce images of soft tissue and doesn't damage living cells
What is Radioactivity?
1. Radioactive Decay: Radioactive substances naturally decay, giving out alpha, beta and gamma radiation
  1. Nuclear radiation causes ionisation by removing electrons from atoms or causing them to gain them
    1. Radioactive decay is a random process, and predicting when a nucleus will decay exactly is impossible
      1. There are so many atoms in even the smallest amount of radioisotope that the average count rate will always be about the same. Radioisotopes have unstable nuclei. Their nuclear particles aren't held together strongly enough
        The half life of a radio isotope is the average time for half the nuclei present to decay. The half-life cannot be changed
2. The nucleus
  1. A nucleon is a particle found in the nucleus. Protons and neutrons are nucleons
    1. Nucleons cannot be lost. Charge is always conserved
3. What are Alpha and Beta Particles?
  1. When an alpha or beta particle is emitted from the nucleus of an atom, the remaining nucleus is a different element
    1. Alpha particles are very good ionisers. They are the largest particles emitted in radioactive decay. This means they are more likely to strike atoms of the material they are passing through, ionising them
      1. Alpha
        An alpha particle is positively charged, has a large mass, is a helium nucleus, has helium gas around it, and consists of 2 protons and 2 neutrons
        During decay its mass number decreases by 4, the nucleus has 2 fewer protons and 2 fewer neutrons, and the atomic number decreases by 2
      2. Beta
        A beta particle is negatively charged, has a very small mass, travels very fast and is an electron
        During decay the mass number is unchanged, the nucleus has one less neutron and one more proton, and the atomic number increases by one

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P4: Radiation for Life

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	Created by Matthew Coombes over 11 years ago