Efficiency - Energy Flashcards
1
Q
What is efficiency?
A
Useful energy and will always be less than 100%
2
Q
What is the equation for efficiency?
A
Useful energy/Total input energy X 100
3
Q
What are some ways to reduce unwanted energy transfers
A
- Lubrication
- Thermal insulation
4
Q
What is lubrication?
A
- Usually liquids that reduce friction
- Friction causes som energy to be dissipated as thermal energy
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
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