Physics - module 2

Physics - module 2

1. light is a type of electromagnetic radiation

2. radiation - transfer of energy

3. visible light - radiation that our eyes can detect - red direction - infared - violet direction - ultraviolet

4. radio waves - microwaves - infared - visible - ultraviolet - xrays - gamma rays

5. energy is delivered as photons - packet of energy

   • not all photos carry the same amount of energy - depends on frequency of radiation
     • increases along EM spectrum -radio wave lowest freq - gamma rays highest freq + most energy

6. em radiation is emitted from a source

7. freq of thermal radiation emitted from an object increases with temperature

8. once emitted all types of em radiation can travel through space/vacuum - all travel at same speed - speed of light

   • speed of light in a vacuum - 300 000km/s or 3 x 10(8) m/s

9. radiation spreads out until it reaches object/matter

   • might be transmitted - keeps going through it
   • could be reflected - bounce back
   • or absorbed
     • objects that absorb - dectectors
     • when radiation is absorbed by matter , photons transfer their energy to matter
       • the energy is deposited by beam of photons depends on how many photons and energy of each
         • the intensity of radiation means how much energy arrived at each square metre of surface per second
           • units = Watts

10. the intensity of a beam of radiation decreases with distance from source bc the beam spreads out and gets partially absorbed when travelling

11. ionisation

    • when a photon hits an atom or molecule, it sometimes has enough energy to remove an electron and change atom or molecule
    • changed atom or molecules can go on to initiate other chemical reactions - chai reaction
    • a lot of energy needed - ultraviolet, xrays, gamma rays can do this
    • if cells are exposed to ionising radiation - damage to DNA can cause mutations - cells dividing over and over - cancer
      • high does can kill cells
    • uv - sun - ionising - damage cells - skin cancer or burns - increase exposure - more damage
    • protect against uv - clothes, suncream
    • protect against xrays -lead shields, concrete
    • xrays - used in hospitals and airports - pass through flesh absorbed by bone and metal

12. heat

    • non - ionising - doesnt have enough energy to change atoms - when it is absorbed it transfers energy to atoms - heats them up
      • more intense, longer exposure - greater heating effect
    • can damage living cells
    • cook food - ovens - infared - microwave --
      • microwaves - vibrate particles - heat up. some strongly absorbed by water molecules - so heat up things containing water. More powerful, higher intensity, less time
        • metal and glass - reflect and absorb to stop microwaves getting out
    • health risks of microwaves
      • used to send signals in phones and phone masts - emits microwave radiation - absorbed by body - heat up body tissue - cancer? - no evidence - minor risk as radiation low intensity

13. em radiation and atmosphere

    • gases in atmos filter out certain types of radiation - absorb and reflect so never reaches earth - visible and radio waves pass through
    • earth absorbs em from sun - warms earths surface - emits some em back into space - cools us down
    • emitted from earth - infared - heat lower freq -than most radiation emitted by sun bc earth is cooler
      • alot absorbd by co2, methane, water vapour
        • these re-radiate heat in all directions - inc earth
          • atmos acts as an insulating layer - stop earth losing heat at night
            • greenhouse effect - without greenhouse gases in atmos, earth be alot colder - too much = global warmong
    • ozone layer
      • absorbs uv radiation
      • protects us
      • ozone - form of oxygen O(3) - occurs naturally at certain height of atmos
      • when an ozone molecule absorbs uv, splits to O(2) and O - reversible - chemical change each time
      • mostly ozone constant - loss = holes - more uv reach earth - ionising and harmful

14. carbon cycle

    • return co2 into air - respiration in plants & animals and decomposers - all contain carbon - decomposers break it down, respire and produce co2 - burning also releases co2
    • photosynthesis removed co2
    • concentration co2 mostly constant
    • human activities - uses cars and electricity - burning fossil fuels - release co2 - faster than we can remove it
    • pop rising - more houses and food needed - deforestation to a room - increase co2 - fewer trees means less co2 taken out - burn trees adds co2

15. global warming/climate change

    • increase of burning fossil fuels = increase of co2
    • global temp risen - link between co2 + temp
    • link of increasing greenhouse effect - humans causing this
    • changes weather patterns, sea levels
      • floods - ice melting - extreme weather - warmer - affect food production - too hot/wet
    • scientists use computer models - used to explain why climate changing now

16. EM waves & communication

    • infared - tv remote and night vision cameras
      • optical fibres - boucing waves off sides of thin inner core of glass or plastic - reflected repeatedly until emerges other end - light and inafred good bc doesnt weaken and glass doesnt absorb
    • microwave - mobile phones and satellite comm
      • long radiowaves
      • satellite - signal from transmitter transmitted into space - absorbed by satellite dish in space - transmits signal back to earth in diff direction recieved by satellite on ground - made of metal -reflects so can focus on waves not absorb them
    • radio - tv and radio transmissions and radar
      • long distance
        • dont get absorbed by atmos as much
      • short wavelength

17. analogue & digital

    • information is converted into electrical signals - digital or analogue
    • amplitude or freq of an analogue signal varies continuously - can take any value in a particular range
    • digital signals can only take one of a small number of discrete values
      • creates pulses - short bursts of waves - digital reciever will decode pulses to get copy of original signal
      • digital better quality -less noise - analogue difficult to know what is original signal was and if you amplify it you amplify the bkgrd noise too
    • both digital and analogue signals weaken as travel - need to be amplified - also pick up interferences or noise form electrical disturbances or other signals
    • digital - information recieved same as original and can transmit several signals at once using one cable or em wave - send more info
    • bytes