Efficiency - Energy

Question 1

What is efficiency?

Answer 1

Useful energy and will always be less than 100%

Question 2

What is the equation for efficiency?

Answer 2

Useful energy/Total input energy X 100

Question 3

What are some ways to reduce unwanted energy transfers

Answer 3

• Lubrication
• Thermal insulation

Question 4

What is lubrication?

Answer 4

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

Question 5

What is thermal insulation in houses?

Answer 5

• 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

Question 6

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

Answer 6

• 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