Nat 5 Physics Waves and Radiation

Nat 5 Physics Waves and Radiation

1. Nuclear Radiation

   • Atoms are made up of protons, neutrons and electrons
   • Ionisation is when an atoms loses or gains an electron and becomes charged. If it loses an electron is becomes positive and if is gains it becomes negative
   • Atoms can be ionised in many ways. There are three main types of ionising radiation
   • Alpha
     • made up of 2 protons and two neutrons
       • Helium Nucleus
     • very slow and heavy compared to beta and gamma
     • most ionising out of the three
     • stopped by a sheet of paper
     • positively charged
   • Beta
     • fast moving electron
     • smaller and faster than alpha
     • produced when a neutron decays into a proton
     • negative
     • not as ionising as alpha
     • stopped by sheet of aluminium
   • Gamma
     • electromagnetic wave
     • travel at the speed of light 3x10^8 m/s
     • no mass
     • no charge
     • very weakly ionising
     • can only be stopped with a block of lead
   • Isotopes are atoms with the same number of protons but a different number of neutrons
   • Radiation will turn photographic film black
     • Gamma can be detected with a geiger muller tube
   • Safety
     • Limit time exposed
       • Wear protective clothing
         • Hold radiation away from face
   • Uses of Radiation
     • Radiotherapy
     • Medical tracers
     • alpha radiation is used in smoke dectectors
     • monitor thickness of paper- beta
   • Dosimetry is the measurement of the amount of radiation
     • Activity
       • The number of nuclei decaying every second
       • Measure in Becquerels (Bq)
       • activity =number of decays/time
     • Absorbed Dose
       • The amount which is absorbed per 1kg of material
       • Measured in Grays (Gy)
       • Absorbed Dose = Energy/ mass
     • Equivalent Dose
       • Harming effect radiation has on the body
       • Measured in sieverts (Sv)
       • Equivalent Dose = Absorbed Dose x Weighting Factor
         • Weighting factor is how dangerous the radiation is
           • Higher the Weighting factor the more dangerous
             • Found in Data Sheet
   • Half Life is the amount of time it takes for the radioactivity of a substance to half
   • Nuclear Fission/ Fusion
     • Fission
       • When the nucleus of a large atom is split creating two smaller nuclei, neutrons and a large amount of energy
         • Can cause chain reaction
     • Fusion
       • Occurs at very high temperatures. Process of joining two samll nuclei together and releasing a lot of energy
         • Nuclear fusion is better than fission as it is safer, produces less harmful waste, easy to get fuel. However it needs very high temperatures which is very difficult

2. The Electromagnetic Spectrum

   • The elctromagnetic spectrum is a family of waves which are all transverse waves
   • All EM spectrum waves travel at 3x10^8 m/s or 3,000,00,000 m/s
   • Gamma waves are used to kill cancer and are detected by a geiger-muller tube
   • X-rays are used to take photos of your body and are dectected by photographic film
     • Turn photographic film black
   • Ultraviolet can be used to treat acne and too much can cause skin damage
   • Visible light is separated in seven different colours Red, Orange, Yellow, Grean, Blue, Indigo and Violet. (ROYGBIV)
     • Red has a longer wave length than violet
     • Visible light is detected by our eyes and can be used as a laser
   • Infrared us heat radiation and can be dectected by a thermometer
     • Used in medicine as heat treatment and in industry to dry paint
   • Microwaves are detected by an aerial and is used for mobile phones
   • Radio/TV waves are dected by an aerial and carry programmes
   • Gamma has the highest frequency and the shortest wavelength and radio waves have the lowest frequency and the longest wavelength

3. Waves

   • All waves transfer energy
   • Longitudinal waves vibrate in the same direction as the direction the wave is travelling
     • Sound waves
   • In transverse waves the vibration is at a right angle to the direction the wave is travelling in
     • Radio waves, Light waves, water waves
   • Wavelength is the distance from peak to peak or trough to trough
     • measured in metres
       • Symbol- lambda
   • The amplitude of a wave is the height of the wave from the middle point to the peak
     • units vary
   • Frequency is the measure of the number of waves passing a point each second or the number of waves per second
     • frequency= no. of waves/ time
       • measured in hertz (Hz)
       • Symbol is f
   • The period of a wave is the time taken for one wave to pass a point.
     • period = 1/ frequency
       • Symbol is T
       • measured in seconds (s)
   • Wave equation
     • speed= frequency x wavelength
   • Diffraction is the bending of waves round an object
     • The longer the wavelength/ lower the frequency the better a wave diffracts
     • The shorter the wavelength/ the higher the frequency the less the wave diffracts

4. Light

   • When the speed of light changes when it travels from one substance to another it is called refraction
   • If the light travels at an angle to the normal the direction and the speed changes
   • If a ray is travelling from air to glass it bends towards the normal and when it travels from glass back to air it bends away from the normal
   • Long sightedness can be corrected using a convex lense and short with a concave lense
   • Convex lense focuses light to one point
   • Concave lenses spread light out

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