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Science Revision ( R1 + R2 ), Energy and Pressure - Coggle Diagram
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Energy and Pressure
Efficiency
Devices are designed to waste as little energy as possible. This means that as much of the input energy as possible should be transferred into useful energy stores.
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The efficiency of a device is the proportion of the energy supplied that is transferred in useful ways. The efficiency can be calculated as a decimal or a percentage, using the equations:
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Energy transfer
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Radiation
All objects transfer energy to their surroundings by infrared radiation. The hotter the object, the more infrared radiation it emits.
Infrared radiation is a type of electromagnetic wave. Unlike conduction and convection, there are no particles involved. This means that energy can be transferred by radiation when there are no particles, like the vacuum of space.
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Conduction
Conduction is where energy is transferred by the vibrating particles in a substance. The energy is transferred from a hotter region to a cooler region.
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Materials which transfer energy easily from a hot area to a cooler area by conduction are called conductors. Metals are very good conductors.
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Internal energy
When a material is heated or cooled, two changes may happen to the particles within the material:
Chemical bonds between the particles may form, break or stretch. There is a change in the chemical potential store of energy in the material.
The material will heat up or cool down as the particles within it gain or lose speed. There is a change in the thermal store of energy within the material.
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Temperature
The cup of tea has an initial temperature of 80°C and cools to a temperature of 30°C . Energy has transferred to the surroundings.
Thermal energy store
Hot tea has more energy in its thermal energy store than cold tea. As the tea cooled, the average speed of the particles in the tea reduced.
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Energy has transferred from the thermal energy store of the tea to the thermal energy store of the surroundings.
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Thermal equilibrium
If there is a difference in temperature between two objects, energy transfers by heating from the hotter object to the cooler one.
The greater difference in temperature, the faster the energy is transferred.
Insulation
Insulation is used to reduce unwanted thermal energy transfers and maintain the temperature of an object.
For example, an insulated picnic bag can keep your lunch cooler for longer. It can also keep hot food hotter for longer.
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Heat
Hot versus cold
The hotter an object, the more energy it has in its thermal energy store .
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Temperature is how hot a substance is. Temperature is commonly measured in degrees Celsius (°C) using a thermometer.
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Wasted energy
Devices waste energy for various reasons including friction between their moving parts, electrical resistance, and unwanted sound energy.
Devices can be made more efficient by reducing the energy that they waste or dissipate to the surroundings. One example is lubrication being used to reduce the friction between moving parts of a machine.
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