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Conversions between units in the metric system are defined by their prefixes (for example, 1 kilogram = 1000 grams, 1 milligram = 0.001 grams) and are thus not listed in this article. Exceptions are made if the unit is commonly known by another name (for example, 1 micron = 10 −6 metre).
A composite input unit consists of two standard units, where the second is a subdivision of the first. For example, |2|ft|6|in may be used to specify 2 feet 6 inches as the input unit in a conversion. See the Input multiples section. Composites are defined in pairs, but any number of pairs can be used to specify an input.
Useful output energy is always lower than input energy. Efficiency of power plants, world total, 2008. Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radiation ...
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property.
hold without the introduction of unit conversion factors. Once a set of coherent units has been defined, other relationships in physics that use this set of units will automatically be true. Therefore, Einstein 's mass–energy equation , E = mc 2 , does not require extraneous constants when expressed in coherent units.
An input unit can be converted to any number of output units—the outputs are specified as a "combination" by separating unit codes with a space (" ") or a plus ("+"). Using a space as a separator does not work if any of the unit codes contains a space.
The energy factor metric only applies to residential water heaters, which are currently defined by fuel, type, and input capacity. [5] Generally, the EF number represents the thermal efficiency of the water heater as a percentage, since it is an average of the ratio of the theoretical heat required to raise the temperature of water drawn to the amount of energy actually consumed by the water ...
distance per vehicle per unit fuel mass; e.g., km/kg. [11] distance per vehicle per unit energy; e.g., miles per gallon equivalent (mpg-e). Energy consumption (reciprocal efficiency) [3] is expressed terms of fuel consumption: [2] volume of fuel (or total energy) consumed per unit distance per vehicle; e.g. l/100 km or MJ/100 km.