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P1 - 1

Heat Transfer
1. Conduction
  1. Particles oscillate
  2. Best in solids
    1. Particles close together
  3. Worst in gases
    1. Particles spread out
2. Convection
  1. Convection Currents
    1. Hot air rises
    2. Cold air falls
    3. Can't form in small spaces
  2. Stopped by solids
  3. Most effective in gases
3. Radiation
  1. Transferred by electromagnetic waves
  2. Stopped by reflective surfaces
4. Insulation/Insulators
  1. Cavity Wall Insulation
    1. Reflective surfaces prevent Radiation
    2. Air pockets too small for convection currents to form
    3. Mainly gas, conduction is weak in gases
  2. Insulators don't conduct heat or electricity
    1. They stop the heat/electricity from passing through them
  3. Loft Insulation
    1. Stops heat being lost from the loft
Waves
1. Transverse
  1. Wave goes up and down while going along
2. Longitudinal
  1. Wave goes in and out
3. Light
  1. Reflection
    1. Light hitting a shiny surface and being reflected
    2. Angle of Incidence = Angle of Reflection
  2. Refraction
    1. Ray of light changes direction
    2. Wave changes speed
    3. Less dense material -> More dense material
  3. Total Internal Reflection (TIR)
    1. When the angle of Incidence is bigger than the critical angle
    2. Light is reflected instead of passing through
  4. Optical Fibres
    1. Uses TIR
    2. Long, flexible transparent glass with a small diameter
    3. Used for communication
    4. Quick speed
  5. Lasers
    1. Intense beam of light
    2. Light waves all:
      1. In Phase- Peaks and troughs of each wave line up
      2. Same frequency
      3. Do not Diverge
      4. Coherent + Monochromatic
4. Diffraction
  1. Wave spreads out when it passes through a space the same size as the wavelength
  2. Can also happen if the wave passes an obstacle
5. Electromagnetic Spectrum
  1. Gamma, X-Ray, UV, Visible, Infra red, Microwaves, Radio Waves
    1. High frequency -> Low frequency
    2. Short wavelength -> Long wavelength
  2. Transverse wave
Cooking
1. Infra red cooking
  1. Toaster, hob or an oven
  2. Hotter objects emit more infra red than cooler ones
  3. Food particles absorb the infra red
  4. Black absorbs infra red better than a paler one
  5. Shiny objects reflect infra red so they don't get hot easily
2. Microwaves
  1. Penetrate about 1cm into the food
  2. Absorbed by water and fat molecules
  3. Cook food quicker than infra red
  4. Shiny metal reflects them
  5. Food should be stirred so that the heat can be spread around
3. Particles
  1. Gain kinetic energy
  2. Surface of the object
  3. Conduction used to transfer the heat through the food so that it it cooked through
Communication
1. Light is fast but normally requires optical fibres
2. Radio can travel far but signal can be lost
3. Electricity is reliable and signals can be boosted but requires wires

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	Created by Charlotte H over 8 years ago