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# 2.5 efficiency

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### 2.5 efficiency

1. 1. 20 October 2010 2.5 Efficiency What are the three types of heat transfer. Which states of matter do they work in?
2. 2. Aims • Understand the efficiency of energy transformations • Calculate efficiency from given data
3. 3. Efficiency • Often a lot of the energy that goes into a system is wasted, mainly as heat • To save energy and money, manufacturers are developing appliances that make better use of energy and therefore waste less • We describe these as energy efficient
4. 4. Efficiency equation useful energy output efficiency (%)  (100%) total energy input
5. 5. Worked example • The energy input per second to a desk lamp with a standard tungsten filament is 100 J and the output is 5 J. Energy expressed as joules per second is the power, which has the unit of watts (W). How efficient is the lamp?
6. 6. useful energy output efficiency (%)  (100%) total energy input 5J  100% 100J  5%
7. 7. Activity A: Write down the ways in which a petrol engine wastes energy
8. 8. Activity B: what is the efficiency of a lamp if the useful energy given out each second is 60 J with 100 J of energy put it.
9. 9. Saving our worlds resources • Our sources of energy can be separated into renewable and non-renewable • Renewable can be replaced, non-renewable cannot.
10. 10. Type Source Energy Uses Powering vehicles, Non-renewable Fossil Fuels heating homes, generating electricity Thermal energy from Non-renewable Generating electricity fission Kinetic energy Renewable Wind transferred to turbines Crops are fermented to make ethanol. Biofuels Ethanol can then be Powering cars burned to give thermal energy Thermal energy Renewable Sun captured by solar panels
11. 11. Type Source Energy Uses Powering vehicles, Thermal energy from Non-renewable Fossil Fuels heating homes, burning fuels generating electricity Thermal energy from Non-renewable Nuclear Generating electricity fission Kinetic energy Renewable Wind transferred to Generating electricity turbines Crops are fermented to make ethanol. Renewable Biofuels Ethanol can then be Powering cars burned to give thermal energy Thermal energy Heating water in Renewable Sun captured by solar homes, generating panels electricity
12. 12. Assessment activity 2.5 • See sheet