Unit 1 - Energy And Efficiency Flashcards
A Hoover has a power of 2kW. What does this tell y about the device?
It transfers 2000J of energy every second.
A Hoover has an efficiency of 75%. What does this tell you about the device?
That 75% of the total energy it uses is transferred usefully, 25% is wasted.
What happens to wasted energy from a device?
It warms up the surroundings.
If a device needs 400J of energy to work, how much does it transfer?
Exactly the same amount. Energy can not be created or destroyed, just changed to different forms and moved to different places.
Why is wasted energy less useful?
It becomes increasingly spread out.
Which two factors affect the amount of energy a device transfers?
Its power.
How long the device is on for.
Name the diagram used to determine the efficiency of a device.
A Sankey diagram. The width of arrows tells us the amount of energy transferred. Counting squares or measuring width with a ruler allows the amount of energy to be found.
Give the useful energy transfer occurring in a lawn mover.
Electrical energy to kinetic energy.
Give the energy transfer occurring from a diver as she falls into the water.
Gravitational potential energy transferred to kinetic energy then to sound and heat energy.
What is payback time?
The amount of time taken before the energy saved by the device = the amount of money spent on the device.
How can a device be made more efficient?
Some of the wasted energy is generates is used for useful purpose. Like the heat from a power station being used to heat local homes and businesses.
Give two reasons for changing all filament bulbs in your house to LED lighting.
It will save money in the long run.
They last a lot longer.
They use less energy and so reduce carbon dioxide emissions, hence add less to global warming.
What does efficiency mean?
How much useful energy is transferred as a proportion of the amount of energy given overall.
