Energy for the Home

Energy
1. Energy flow
  1. Hot body to cold body
  2. Energy decreases as energy flows out
2. Measuring temperature
  1. Specific Heat Capacty
    1. Amount of energy needed to raise 1kg by 1°C
    2. J/kg °C
  2. Energy transfer by Specific Heat Capacity:
    1. Energy transferred = mass x spec. heat capacity x temp. change
3. Specific Latent Heat
  1. Energy needed to melt/boil 1kg of a material
    1. Measured in (J/kg)
      1. When changing states, energy is transferred but temp. remains constant
        Energy is used to break intermolecular bonds instead
    2. Energy transfer = mass x specific latent heat
    3. E.g. Water SLH = 340,000
Insulation
1. Double glazing
  1. Reduces heat lost by convection
  2. two glass panels filled with vaccum OR gas
    1. E.g. argon
2. Loft insulation
  1. Reduces heat lost by conduction and convection
  2. Hot air in home rises
  3. Stops energy transfer between ceiling to loft AND ceiling to roof
3. Cavity Wall
  1. Reduces conduction and convection
    1. Air in foam insulates
    2. Air is trapped by foam
4. Insulation blocks
  1. Shiny foil on either side
    1. Reflects sun's energy back during summer
    2. Home's energy is reflected inward during winter
Conduction, Convection, Radiation
1. Conduction
  1. Kinetic energy between particles
2. Convection
  1. Gas expands when heated
    1. Makes it less dense so rises
      1. Density in kg/m3 OR g/m3
      2. Density = Mass/Volume
3. Radiation
  1. Needs no medium
  2. Travels through vacuum
Energy Efficiency
1. efficiency = useful energy output (x100%) / total energy input
2. Shown by Sankey diagrams
  1. Source energy is lost to 'sink'
3. Different insulation types vary in cost and efficiency
  1. Payback time = Cost of Insulation / Annual Saving
  2. All things waste some energy
4. Efficient buildings lose little energy to surroundings
  1. Designers and architects consider this
Waves
1. Wave Terms;
  1. Amplitude = maximum displacement from rest position
  2. Crest = Highest point
  3. Trough = Lowest point
  4. Wavelength = Distance between two successive points
2. Wave speed = Frequency x Wavelength
3. Measurements
  1. Frequency: Hertz (Hz)
  2. Wavelength: Metres (m)
  3. Speed: Metres/second (m/s)
4. Types & Properties
  1. Radio
  2. Microwave
  3. Infra-red
  4. Visible
  5. Ultra-violet
  6. X-ray
  7. Gamma
5. Changing Waves
  1. Refraction
    1. Occurs as wave enters a denser medium
      1. Wave speed changes
        (Frequency stays same but wavelength changes)
  2. Diffraction
    1. Wave spreads out after passing through gap
      1. 90° when wavelength = gap size
    2. Noticeable in telescopes and microscopes
6. Cooking and Communicating
  1. Infrared doesn't penetrate food well
  2. Microwaves penetrate 1cm
    1. Reflected by special glass
  3. EM Spectrum
    1. Energy transfer depends on
      1. Wavelength
      2. Frequency
      3. High frequency (short wavelength) transfers more energy
  4. Microwave lengths
    1. Between 1mm and 30cm
    2. Mobile phones = longer wavelengths
      1. Transfer less energy
  5. Microwave communication
    1. Used over long distances
      1. Transmitter + receiver need line of sight
        E.g. top of high buildings
    2. Satellites are used
      1. Signal recieved from Earth
        Amplified
        Retransmitted to Earth
    3. Signal strength
      1. Little diffraction
        Strong weather and large water bodies scatter signals
      2. Curvature of earth
        Limits line of sight
        Transmitters must be high up/near
    4. Interference with equipment
      1. Bannings
        Hospitals
        Planes
Light and Lasers
1. Morse Code
  1. Series of dots and dashes
    1. A digital signal
2. Signals
  1. Can be sent by Electromagnetic Spectrum or electricity:
    1. Almost instantaneous
    2. Criticising each method
      1. Speed?
      2. Can it be seen?
      3. Can wires be cut?
      4. How far must it travel?
3. Laser Light
  1. Single frequency
    1. (White light has many at once)
  2. In phase (Syncronised)
    1. White light is mixed)
  3. CDs
    1. Surface is pitted
      1. Pits = digital signal
    2. Laser shone on surface
      1. DIfferent reflections provide signal
4. Critical Angles
  1. More dense --> Less dense
    1. °Refraction > °Incidence
  2. When °Incidence makes °refraction = 90°
    1. That °incidence is 'critical angle'
      1. When °Incidence is GREATER than critical angle
        Total internal reflection occurs (TIR)
  3. Use in communicatinons
    1. Fibre optics
      1. Telephone
      2. Computer
      3. Data travels at speed of light (200,000km/s in glass)
5. Endoscopy
  1. Light sent down optical fibres
    1. Reflects off patient's insides
      1. Light is picked up by endoscope
Data Transmission
1. Infrared signals for electronics
2. LED pulses a digital IR signal
  1. Start command
  2. Instruction command
  3. device code
  4. Stop command
3. Analogue/Digital switch
  1. 2009 - 2015
  2. Greater program choice
  3. Interaction
  4. Subtitles
4. Digital Signal advantages
  1. No damaging interference from other waves
  2. Multiplexing
    1. Multiple waves combined and sent together
Wireless Signals
1. Less atmospheric refraction at high frequencies
2. Digital Audio Broacasting (DAB)
  1. Greater range
  2. Eliminates interference
3. Radio reflection
  1. Reflected by the Ionosphere
  2. Signal can pass around Earth
4. Microwaves pass through Ionosphere
  1. Comms. satellites
    1. Geostationary orbit
5. Problems
  1. Radiowaves diffract
  2. Satellites require focused signals
    1. Beams split (diverge)
Stable Earth
1. Earthquakes
2. Ozone Depletion
  1. Found in Stratosphere 10km - 30km up
  2. Filters UV
  3. Chlouroflourocarbons (CFCs)
    1. Depletion highest at the poles
  4. Monitored using IR satellites

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Energy for the Home

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	Created by Oliver Wood about 11 years ago