Efficiency Flashcards
what happens when there is a change in a system?
energy is transferred and some of that energy is dissipated.
what is a rise in temperature in mechanical processes caused by? (2)
- transfer of wasteful energy in mechanical processes.
- energy is then dissipated into the system.
what causes energy to be dissipated in a mechanical system?
-when two surfaces rub together.
how is energy dissipated in a mechanical system? (3)
- work is done against friction which causes heating of the two surfaces
- so internal (thermal) energy store of surfaces increases
- this is then transferred to internal energy store of the surroundings
useful and wasteful energy in an electrical kettle: (3)
Useful energy:
Energy that heats the water.
Wasted energy:
Internal (thermal) energy heating the kettle.
Infrared radiation transferred to the surroundings.
useful and wasteful energy in an hairdryer: (5)
Useful energy:
Internal (thermal) energy heating the air.
Kinetic energy of the fan that blows the air.
Wasted energy:
Sound radiation.
Internal (thermal) energy heating the hairdryer.
Infrared radiation transferred to the surroundings.
useful and wasteful energy in a light bulb: (2)
Useful energy:
Light radiation given out by the hot filament.
Wasted energy:
Infrared radiation transferred to the surroundings.
useful and wasteful energy in a tv: (4)
Useful energy:
Light radiation that allows the image to be seen.
Sound radiation that allows the audio to be heard.
Wasted energy:
Internal (thermal) energy heating the TV set.
Infrared radiation transferred to the surroundings.
describe a method of reducing wasted energy in a mechanical system: (1)
lubrication
how does lubrication reduce the wasted energy in a mechanical system?
reduces friction between moving parts of machine., thereby reducing thermal energy transferred.
describe a method of reducing wasted energy in a thermal-transferring system, and why would this specific method work in this instance?
- thermal insulation
- a material would not be able conduct heat, and thereby less thermal energy will be wasted
what is the difference between an efficient and inefficient device?
an efficient device would waste very little of its input energy, whilst an inefficient device will waste a large quantity of its input energy
what is efficiency?
How good a device is at transferring energy input to useful energy output
what is the efficiency of a device the proportion of?
the energy supplied that is transferred in useful ways
equation for calculating efficiency:
(useful output energy/ total input energy) (x 100)
why is it not possible to have an efficiency greater than 1/ 100%? (3)
more energy is being transferred than is being supplied,
which would mean that energy is being created.
this breaks the law of conservation of energy
how can the efficiency of any device be increased?
by reducing wasted energy transfers so more of the input energy is usefully transferred
why is efficient heating of buildings important in reducing the amount of energy used?
this is because the amount of energy required for heating can be very large.
where will thermal energy transfer from the inside of warm buildings into the surroudings?
thermal energy will transfer from inside warm buildings to the cooler surroundings
which materials are most appropriate for building warmer houses? such as?
poor conductors (brick, wood, plastic & glass)
why would a house built out of conducting materials be difficult to live in?
it would be extremely cold as energy would be able to leave the house easily.
what is thermal conductivity?
a measure of how well a material conducts energy when it is heated
how can thermal conductivity be applied to how many Watts are transferred through a material?
‘x’ amount of joules (J) of energy will flow per second through a cubic block of ‘x’ material (1 m × 1 m × 1 m) when the temperature difference between its sides is 10°C.
how can we reduce the thermal energy transferred from a warm house? (4)
- walls can be built thicker
- so the energy must travel further before it is transferred to the outside.
- thermal energy transfers can be reduced further if there are two walls with an air gap between them
- as air has a lower thermal conductivity than brick. This is known as a ‘cavity wall’.
why is it better to have a window made of two layers of glass with a layer of air trapped between them? (3)
-both glass and air are insulators because they have low thermal conductivities.
-layer of air has the lowest thermal conductivity and reduces the overall conductivity of the window unit.
(-since air and glass are both transparent people can still see through the window.)
