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Energy (Types of energy (Light, Electrical, Sound, Gravitational Potential…
Energy
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Efficiency
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Efficiency does not have a unit as it is a ration. It is always a number between 0 and 1. This number represents the fraction of the energy that is converted to the form of energy we want.
Example
A 60W lamp uses 60J of energy every second. It is 5% efficient. How much useful light energy does it emit per second.
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Heat Transfers
Thermal Conduction
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In a hot substance the particles have more kinetic energy. The more energetic particles transfer their heat to particles near them. Therefore gain energy and pass the energy onto particles near them.
Convection
The transfer of heat through fluids by the upward movement of warmer, less dense regions of fluid
Heated particles expand and become less dense than the colder ones surrounding them, so rise to the top. Colder particles sink to fill their space and are then heated up too. At the top the warm water starts to cool, become less dense and begins to sink, so a circulating current is setup. This is called convection current
Radiation
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IR waves can be reflected and absorbed by different materials. Highly polished, shiny surfaces are good reflectors of thermal radiation. Matt black and dark surfaces are poor reflectors or good absorbers of heat radiation
Transfer and conversion
For energy to be useful we must be able to transfer and convert it when ever we want to. Unfortunately when doing so some energy is converted to unwanted forms called waste energies.
Unwanted energy reduces efficiency. This problem is the same whether the system is small like a car, or large like nationwide electricity generating.
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