Physics P4

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Sparks - P1


  • An atom consists if small positively charged nucleus surrounded by an equal number of negatively charged electrons
  • In a stable atom, the charge is neutral
  • Electrostatics is due to the movement of electrons
  • Like charges repel, unlike charges attract
  • When a polyethene rod is rubbed with a duster, electrons are transfered into the polyethene, making it negatively charged
  • When an acetate rod is rubbed with a duster, electrons are transfered into the duster, making the acetate positively charged
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Sparks - P2

Electrostatic Shocks

  • When inflamable gases or vapours are present, or there is a high concentration of oxygen, a spark from static electricity could cause an explosion
  • If a person touches something at a high voltage, large amounts of electric charfe may flow through their body to ther earth
  • Even small amounts of charge can be fatal
  • Electric Shocks can be avoided by...
    • Connecting an earth wire
    • In a factory, an opperate can stand on an insulating mat, normally made of rubber
    • Shoes with insulating soles can be worn 
  • Anti-static sprays can be purchased. These prevent a build up of charge.
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Uses of Electrostatics - P1

Dust Precipitators

  • Removes harmful particles from the chimneys of factories and powerstations
  • A metal grid is placed in the chimney and  is given large charge from a high voltage supply
  • Plates inside the chimney are earthed and gain the opposite charge to the grid
  • As the dust passes the grid it become charged the same way. Because unlike charges attract, it then sticks to the oppositely charged plates
  • At intervals the plates are vibrated so the dust falls into a collector

Paint Spraying

  • The spray gun is charged
  • All the particles are then charged the same
  • The object is given the opposite charge to the paint
  • Because unlike charges attract, the paint sticks to the object
  • This means the object gets an even coat, with limited paint wasted
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Uses of Electrostatics - P2

Problems with Paint Spraying

  • The object becomes charged from the paint, meaning further paint droplets are repelled away from the object


  • It is a procedure to restore regular heart rhythm through recieving an electric shock
    • The paddles are charged from a high voltage supply
    • They are then placed on the pacients chest 
    • Electric charge is passed through the patient
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Safe Electicals

Live, Neutral and Earth Wires

  • Live wire carries high voltage around the house
  • The neutral wire completes the circuit
  • The earth wire is connected to the base to stop it from becoming live
  • A fuse contains a wire which melts if the current is too large
  • Earth wires stop a person from recieving an electric shock if they touch a faulty appliance
  • A re-set able fuse doesn't need to be replaced to restore power, it can be re-set
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Resistance and Power


  • The rheostat changes the resistance
    • Voltageup,currentup
    • Resistanceup,currentdown
  • Formula for resistance: 
    • resistance = voltage / current

Electrical Power

  • power= voltage x current
  • This can be used to calculate the correct fuse
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  • Ultrasound is a sound about 20,000Hz which is a higher frequency than humans can hear
  • It is a pressure wave containing compressions and refreactions
  • compressions are refgions of higher pressure and refractions are regions of lower pressure
  • The features of longitudinal sound waves are...
    • they can't travel through a vacuum
    • The denser the medium, the faster it travels
    • the higher the pitch the shorter the wave length
    • the more powerful the ultrasound, the more energy the wave carries and the larger the amplitude
  • In a longditudinal wave, the virations 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 waves 
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Uses of Ultrasound - P1

When ultrasound is used to break-down kidney stones..

  • a high-powered ultrasound beam is directed at it
  • the ultrasound breaks the stone into smaller pieces
  • tiny pieces are then excreted from the body normally
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Uses of Ultrasound - P2

When ultrasound is used in a body scan...

  • At each boundry between different tissues some is reflected and the rest is transmitted
  • The different echos mean different body parts
  • The returning echos are recorded and used to build up an image

Ultrasound can be used because... 

  • Different body structures can be calculated using speed= distance / time. Knowing the different speeds helps to build a picture
  • It can produce an image of soft tissue
  • It doesn't damage cells
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Radioactive Decay

Radioactive Decay

  • Radioactive substances decay naturally giving out alpha, beta and gamma particles
  • This causes ionisation by removing electrons from other atoms
  • This process is random so it's impossible to predict
  • The half-life is the average time for half the nuclei present to fade away
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What is "alpha"?

  • Properties
    • positively charged
    • large mass
    • helium nucleus
    • has helium gas around it
  • During Decay...
    • the mass number decreases by 4
    • nucleus loses 2 neutrons and 2 protons
    • atomic number decrease by 2

<- equation for decay

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What is "beta"?

  • Properties
    • negatively charged
    • is an electron
    • has a very small mass
    • travels very fast
  • During Decay...
    • mass number is unchanged
    • nucleus has one more proton
    • atomic number increase by 1

(<- equation for decay

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Uses of radioisotopes


  • When using a tracer to locate a leak in an underground pipe...
    • A very small gamma emitter is put into the pipe and dector is passed along the group above the pipe
    • An increase in radiation is detected at the leak and no where else after
  • Gamma sources are used as they can penetrate the surface

Smoke Detectors

  • A smoke dector contains a radioisotope which emmits alpha radiation. Without smoke, the alpha particles ionises the air, which creates current. With smoke, there is no current so the alarm goes off

Radiocarbon Dating

  • Carbon-14 is present in all living things. By measuring the amount, of Carbon-14, the aproximate age can be found. (When something dies, no more of this substance is produced so the amount decreases)
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Dating Rocks

  • Some Rocks Contain Uranium
    • This decays leaving a stable isotope of lead
    • By comparing the amound of uranium in a rock sample, its approximate age can be found

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Using Radiation

  • Alpha radiation is absorbed by the skin so is not good for medicine
  • Beta passes through the skin and not the bone. It's medical uses are limited.
  • Gamma radiation is used in medicine. Cobalt-60 is generally the radioactive substance used to treat cancer
  • When nuclear radiation passes through a material it causes ionisation. This increases your risk of cancer
  • Cancer cells can be destroyed to exposing the the tumor to large amounts of radiation. This is called radiotherapy
  • Materials can be made radioactive  when thier nuclei absorbed extra neutrons in a nuclear reactor

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Comparing x-rays and gamma rays

  • When x-rays pass through the body the tissues absorb some of the radiation. This amount depends on the density of the absorbing material
  • Gamma rays have similar wavelengths to x-rays be are produced in different ways
  • X-rays are made by firing high-speed electrons by metal targets 
  • An x-ray machine allows the rate of production and the energy to be controlled, but you can't change this with gamma radiation


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  • A radioactive tracer is used to investigate inside a patients body without surgery
    • Technetium-99m is a commonly used tracer It emmits gamma radiation
    • Iodine-123 emmits gamma. It is commonly used to investigate the thyroid gland.
    • The radioactive tracer is either mixed with food OR injected into the body
    • The progress is monitered through the body by a computer or gamma camera

Treating Cancer

  • A radioisotope is used to destroy a tumor in the body
  • Three sources of radiation (each with 1/3 of the dose) and placed around the patien twith the tumor at the centre
    • This also limits tissue damage
  • Radiation is then slowly rotated around the patient, so the tumor recieves constant radiation
    • This also means the tissue recieves less of a dose
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Nuclear Power Stations

  • Uranium consists of 2 isotopes uranium-235 and uranium-238
  • Enriched uranium is used as a fuel in nuclear powerstations
  • Fission occurs when a large unstable nucleus is split up and energy is released
    • The heat is used to boil water and produce steam
    • The pressure turbs a turbine
    • This ritates a generator
  • With Uranium fission, a chain reaction occurs
    • A nuclear bomb is an example of an uncontrollable one
  • In a nuclear powerstation, atoms of uranium-235 are bombarded with neutrons. This causes the nucleus to split an release energy 


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Controlling Nuclear Fission

  • the output can be controlled by...
    • a graphite moderator can be put between fuel rods to slow down the fast moving neutrons during fission
    • Boron control rods can be raised an lowered

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  • Nuclear fussion happens when two light nuclei fuse together releasing large amounts of energy 
    • Requires high tempratures
    • Research in this venture is expensive so it is a multi-national venture
  • In stars, fusion takes place under high tempratures & pressures
  • Fusion bombs are started with a fission reaction which creates a high temprature needed for fusion
  • So far attempts to replicate this on earth have been unsuccessful
    • Scientists are trying to solve this safely
    • Cold Fusion is still not excepted as realisitic since any results are impossible to verify
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