P2 - Radiation and Life

P2 - Radiation and Life

1. Electromagnetic Radiation

   • Radiation is a transfer of energy.
   • There are seven types of radiation altogether:
     • Radio Waves | Micro Waves |Infra-red | Visible Light | Ultra-violet | X-Rays | Gamma Rays
       • Increasing energy and frequency ----------------------------------->
   • All transfer energy
     • This energy is delivered as photons (a packet of energy)
       • The amount of energy carried depends on the frequency of the radiation.

2. EM Radiation and Energy

   • Many objects emit electromagnetic radiation e.g. the sun, mobile phones etc
     • This is called a source
     • The frequency of thermal radiation emitted from an object, increases with temperature
     • All types of EM radiation can travel through space (a vacuum) and they all travel at the speed of light
       • 300,000 km/s
   • When radiation is emitted, it spreads out until in reaches some matter and can:
     • It can be transmitted- it keeps going e.g. light passing through glass
     • It can be reflected- bounce back e.g. a mirror
     • Or it can be absorbed e.g. a sunbather absorbing UV rays from the sun
     • Two or three of these things can happen at the same time
   • Intensity decreases as distance from the source increases
     • Total energy= Number of photons x energy of each photon
     • Units of intensity are Watts per square metre
     • The photons spread out. Some photons are absorbed as they travel

3. Ionisation

   • Some EM Radiation causes Ionisation
     • When a photon hits an atom or molecule, it sometimes has enough energy to remove an electron and change the atom or molecule
     • Ultra violet, X-Rays, Gamma Rays because they have enough energy to do this
   • This can be dangerous if it happens to cells because it can mutate DNA and cause cancer
     • Very high doses of radiation can kill cells altogether
     • UV Radiation from the sun is ionising and can lead to sun burn and skin cancer
   • We need protection against this dangerous radiation
     • We can use sun cream and clothes to protect us from the sun
     • Radiographers wear lead aprons and stand behind concrete when doing X-Rays

4. Uses of EM Radiation

   • When it's absorbed by a substance, it transfers energy and heats it up
     • This effect could damage living cells e.g. getting burned
     • Ovens use infra- red radiation to cook things
     • Microwave ovens use microwaves to heat things
       • Microwaves are strongly absorbed by water molecules so can heat up all food
       • Microwaves have metal cases and screens which reflect and absorb microwaves to we don't absorb them
   • Microwaves are used to send signals between mobile phones
     • When you make a call, a small amount of radiation is emitted from the phone.
       • This causes concerns of the heating of tissues like the brain and jaw which can increase the risk of medical conditions
         • However, the radiation is low intensity and there isn't much evidence that is does affect our health

5. EM Radiation and the Atmosphere

   • The gases in the atmosphere absorb or reflect the radiation so it doesn't reach the Earth's surface
     • But visible light and radio waves pass through easily
   • The Earth emits infra red radiation and is absorbed by atmospheric gases
     • Carbon dioxide, methane and water vapour etc.
     • These gases re-radiate heat in all directions including back to Earth.
       • The atmosphere acts as an insulating layer, stopping the Earth losing all its heat at night.
         • This is known as the Greenhouse Effect
   • In the atmosphere there is a gas called Ozone (O3) which absorbs UV
     • It protects us from too much UV Radiation
     • Ozone is formed when an O2 molecule bonds with a single oygen atom
       • UV Radiation splits the O3 molecule into an O2 and an Oxygen atom- so the reaction is reversiible
     • Loss of ozone can cause holes in the ozone layer and more UV radiation would reach us on Earth which is potentially dangerous

6. The Carbon Cycle

   • Two of the greenhouse gases which keep Earth Warm are:
     • Carbon Dioxide and Methane
       • They both contain carbon
   • All the carbon on Earth moves in a big cycle
     • Processes that return Carbon Dioxide to the atmosphere are:
       • Respiration in Plants and Animals
       • Respiration in Decomposers (bacteria and fungi)
       • Burning e.g. trees or coal
     • Photosynthesis removes carbon dioxide from the atmosphere
     • These processes are meant to balance each other out
   • The concentration of Carbon Dioxide is increasing due to:
     • More cars, planes, electrical gadgets which need energy from fossil fuels
     • Population is rising
       • More houses built, more food grown
       • Chopping and burning trees down

7. Global Warming and Climate Change

   • Evidence shows that the rise in carbon dioxide levels is causing global warming by increasing the greenhouse effect
     • Humans are causing global warming
     • Global warming is a type of Climate Change
   • Scientists use computer models to understand climate change
     • A climate model is a load of equations linking these various parts of the climate system
     • It uses some data to work out something about the climate around the world
     • They can also be used to explain why the climate is changing now
       • Climate modelling over the last few years shows that natural changes (from changes in our orbit) don't explain the current 'global warming' so must be due to human activity.
   • The consequences of Global Warming can be very serious
     • Sea levels rise due to it getting warmer and expanding
       • Flooding
     • Ice melting
       • Rise in sea levels
     • Changed weather patterns
       • More extreme weather
       • This will affect food production

8. EM Waves and Communication

   • EM Radiation can be used to send information
     • Infra red- TV Remote controls and night vision
     • Microwave- Mobile phones and satellite communication
     • Radio- TV and Radio transmissions and radar
   • Radio and Microwaves are good at transmitting information over long distances because they are not as easily absorbed by the Earth's atmosphere
   • Infra red and light are used in optical fibres
     • Optical fibres work from the wave entering one end of the fibre an being reflected repeatedly until it emerges the other end.
       • Light and infra red are good for this because the glass inside doesn't absorb much of the radiation

9. Analogue and Digital Signals

   • All information is converted into electrical signals before it's transmitted
     • It's sent out as either analogue or digital
   • Analogue signals varies continuously and can take any value in a particular range
   • Digital signals can only take the value of 0 or 1
     • A digital receiver will decode these pulses to get a copy of the original signal
     • Digital signals are far better quality because it is easier to 'clean up' the signal
       • You can also transmit several digital signals at once using one cable or EM wave.
         • This isn't possible with analogue
     • Digital signals are easier to process using computers, since computers are digital devices
   • Both signals weaken as they travel so need to be amplified on their route