AQA GCSE Wasted Energy
Energy terms:
Input energy: Energy supplied to a device or machine.
Useful output energy: Energy that is transferred into a useful form.
Wasted output energy: Energy that is transferred to an energy store that is not needed, or is dissipated to the surroundings.
Dissipated means that the energy spreads out to the surroundings, so it becomes less useful.
Example 1
As the boy pedals the bike, the chemical energy store in his muscles is transferred mechanically to the kinetic energy store of the bike.
The input energy store = chemical energy store
Useful output = kinetic energy store
At the same time there is friction between the moving parts of the bike and between the bike wheels and the road surface. So, some of the chemical energy store is transferred to thermal energy store mechanically. This would be a wasted output energy, which then dissipates to the surroundings.
Sound is also heard from the bike, because some of the chemical energy store is transferred by radiation to sound waves, this is also considered as wasted energy and dissipates to the surroundings.
Oil, or grease can be used on the moving parts to reduce friction, this would make the energy transfer more efficient as more of the chemical energy store would be converted to kinetic energy store
Example 2
The washing machine contains an electic motor, which uses electromagnetism to rotate the drum.
Input energy store is magnetic energy
Useful output energy store is kinetic energy, due to the rotation of the drum
Wasted output energy store is thermal energy, due to resistance of wires in the motor, some of the magnetic energy store will be converted to thermal energy store and then dissipated to the surroundings.
Using lower resistance wires, such as thicker wires, or wire with a higher electrical conductivity could make the energy transfer more efficient. This means that more of the magnetic energy is converted to kinetic energy, less to thermal energy store.
One more point, thermal energy store being classed as wasted, is ok, providing that the washing machine is carrying out a cold wash!
Example 3
Houses are mostly heated by gas boilers, which burn natural gas to heat water. The hot water then transfers thermal energy to each of the rooms in order to heat the house.
Input energy is chemical energy store of the natural gas
useful output energy is thermal energy store of rooms
Wasted output energy store in thermal energy store of surroundings, outside of house.
If the house were better insulated the energy transfer would be more efficient. More of the chemical energy store, would be converted to the thermal energy store of the rooms, less would be converted to thermal energy store of the surroundings outside of the house.
Insulation could include cavity wall, loft insulation, double glazing.
Practice Questions
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