- Recall earlier work on energy devices and on burning fuels. Review the paradox that although electricity is clean and safe to use, its generation can have a big environmental impact. Introduce the idea of dissipation of waste energy as an inevitable consequence of many energy transfers; refer to cooling towers at power stations.
- Broaden the issue to looking at use of energy in different ways,
eg
ask pupils to consider how environmentally friendly electric cars really are. (Although electric motors are three times as efficient as internal combustion engines, the electricity has to be generated first.) Compare battery-powered cars (recharged at the mains) with fuel-cell powered models. Compare the energy required to make a car with the energy needed to run it (ratio is approximately 10:1). Is the real issue about replacing old, inefficient cars with new, more energy-conserving ones?
- Use questions to discuss with pupils the difference between tungsten-filament light bulbs and 'energy-saver' bulbs,
eg a 20W energy-saver lamp is said to be equivalent to a 100W filament lamp. Can this be supported? What happens to the other 80W from the filament lamp? (Feel the heat - carefully.)
- Provide information about these lamps,
eg advertising material, and ask pupils to work out whether the purchase of energy-saver bulbs is cost effective.
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- distinguish between useful energy and wasted or dissipated energy
- make comparisons between appliances and devices concerning their efficient use of energy
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