P2 (part one)

P2 (part one)

1. a&b

   • photocells
     • convert light into electricity
     • larger SA, more electricity produced
       • more sunlight can be absorbed
     • useful when mains not avalable
       • remote areas
         • where electricity is expensive
     • produces dc
       • one direction
     • advantages
       • robust
       • little maintenance
       • no fuel required
       • no polluting waste
       • no power cables
       • uses renewable energy resource
       • long-life
     • disadvantages
       • no electricity when dark or bad weather
       • quite expensive
     • light intensity
     • SA exposed
     • distance from light source

2. passive solar heating

   • in the day
     • sun heats floors and walls
   • at night
     • the heat is radiated back from walls and floors

3. greenhouses

   • the sun is very hot
     • so has short wavelength
       • the glass of the greenhouse is transparent to the suns radiation
         • the material absorb radiation and heat up
           • reradiated infrared radiation cos they're are cooler and have longer wavelength
             • reflected back

4. wind power

   • result of sun heating the earth
     • creating convection currents in the earths atmosphere
   • winds ->
     • blades ->
       • generator
   • advantages
     • robust
     • renewable resource
     • dont pollute
   • disadvantages
     • ugly
     • noisy
     • shut down at high wind speeds
     • needs space

5. dynamo

   • generates electricuty
   • increased by: stronger magnetic field, more turns on coil, faster movements.
   • ac- slip rings motor-split rings
   • moving coil near magnet or moving a magnet near a coil
   • coil of wire is free to rotate between the poles of a magnet (close) as coil rotates, it cuts thee magnetic field and a current will pass through the coil a current is induces and movement is essential)
   • freq. no. complete waves passing a point in 1sec
     • the ac from generator has a freq.
   • output can be displayed on an oscilloscope
     • shows how current produced by dynamo changes over time
     • time for one complete cycle is called the period of alternating curent
     • height is the mx./peak voltage
       • length of wave represents time for one cycle
       • frequency (hz) .= 1/period(s)

6. national grid

   • source of energy are power stations
     • fuels are used to heat water
       • water boils to produce steam
         • steam at high pressure turns a turbine
           • turbine drivesa generator
             • generator produces electricity
               • then step-up transformer (less energy loss)
                 • power lines etc.
                   • step-down transformer
                     • consumers (homes, schools, farms etc)

7. greenhouse effect

   • earths atmosphere traps energy; alike a greenhouse
   • atmospheric gases let short wavelength uv to pass through
     • infrared radiation; long wavelength; is radiated back from warmed surface of earth

8. water vapour; carbon dioxide; methane

   • natural sources
     • water vapour
       • evaporation of large bodies (e.g lakes)
       • transpiration
     • carbon dioxide
       • fermentation
       • respiration
       • volcanic eruptions
     • methane
       • decomposition of organic matter (wetlands)
       • formation of fossil fuels (coal)
       • termites
   • manmade sources
     • water vapour
       • 0.001% human activity
     • methane
       • cows
       • rice paddies
       • mining and burning of fossil fuels
       • burying waste on landfill
     • carbon dioxide
       • burning solid fuels (eg. coal/oil/gas)
       • incineration of waste
       • cement manufacture
       • deforestation
   • environmental issues
     • factories produce smoke which reflects radiation from the cities, back to earth, warming it up
     • volcanoes emit ash when they erupt, which stops the suns rays reaching the earth, thus cooling down the earth

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