2.3 and 2.4 Useful Energy/Efficiency Flashcards
What is useful energy out of a machine?
Energy that is transferred to the place we want it to and in the form that we want
What is wasted energy out of a machine?
Energy that is not usefully transferred
What happens to the wasted energy from a light bulb?
It is transferred to the surroundings which get warmer
What happens as the energy spreads out?
It becomes more difficult to use for further energy transfers
Why do the parts of the machine warm up during energy transfers?
There is friction between the moving parts so energy is wasted here and warm them up
Name one way friction between the moving parts of a machine can be useful
In the brakes of a bicycle or a car
Where does the useful energy eventually end up?
Warming up the surroundings
Name the unit that energy is measured in
Joules
What is the energy applied to a machine?
The input energy
What can we tell from the conservation of energy rule? (Addition)
Input energy = useful energy + wasted energy
How can we calculate the efficiency of a machine?
Efficiency = useful energy / input energy
x100 to get a %
In a light bulb, for every 25J applied to the bulb, 5J are usefully transferred into light energy. What is the efficiency of the bulb?
20%
Why can’t any object be 100% efficient?
Energy will always be wasted, usually as heat
Name the one exception of a machine that can be 100% efficient
Electric heater
How is an electrical heater 100% efficient?
It is meant to produce heat so the wasted heat is actually useful
