Efficiency - Energy Flashcards

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1
Q

What is efficiency?

A

Useful energy and will always be less than 100%

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2
Q

What is the equation for efficiency?

A

Useful energy/Total input energy X 100

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3
Q

What are some ways to reduce unwanted energy transfers

A
  • Lubrication
  • Thermal insulation
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4
Q

What is lubrication?

A
  • Usually liquids that reduce friction
  • Friction causes som energy to be dissipated as thermal energy
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5
Q

What is thermal insulation in houses?

A
  • Thick walls made out of low thermal conductivity (slower the rate of energy transfer - building will cool more slowly)
  • Cavity walls - made out of an inner and outer wall with an air gap in the middle, air gap reduces the energy transferred by conduction through the walls
  • Cavity wall insulation - cavity wall air gap is filled with foam - reduces energy transfer by convection in the wall cavity
  • Loft insulation - reduce convection currents created in lofts
  • Double-glazed windows - air gap between 2 sheets of glass prevent energy transfer by conduction through the windows
  • Draught excluders - around doors and windows reduce energy transfer by convection
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6
Q

Explain how cavity wall insulation reduces the amount of energy transferred out the house?

A
  • Reduces energy transfer by convection
  • And conduction
  • because insulating foam has a lower thermal conductivity and so a low rate of energy transfer from thermal stores
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