Energy density
The energy density refers to the physics in the distribution of energy to a certain size and consequently always has the shape
Most often it is used as
- Volumetric energy density, a measure of the energy per unit volume of a substance ( the SI unit: joule per cubic meter)
- Gravimetric energy density or specific energy is a measure of the energy per unit mass of a substance ( the SI unit: joule per kilogram).
But in the end, one can define for each physical quantity corresponding energy density. According to DIN 5485, the term energy density of the dimensional, particularly volumetric information is reserved specifically in mass, specific energy; see " energy " and " size -based ".
Of great practical interest is the energy density at the energy storage devices such as fuels and batteries used in the art. In particular in the automotive industry, the energy density of the energy storage device used is decisive for the achievable range.
- 2.1 Examples
Energy density in electrodynamics
Energy density of electromagnetic waves
From Maxwell's equations it can be concluded that the maximum energy output of electromagnetic waves is proportional to the square of the field amplitude in a fabric. Electric and magnetic field contribute equally:
Energy density in the plate capacitor
The energy of a charged plate capacitor is calculated as
For the capacity
The voltage U is derived from E · d Substituting we obtain for the energy
This leads to the energy density
Energy of the magnetic field of a coil
The energy of the magnetic field of a coil with the magnitude of the magnetic flux density, the cross-sectional area, the length, the number of turns, the current and the magnetic field constant results in.
And then
For the energy density of the flux density.
Energy density of energy storage and primary energy sources
The energy density of fuels called calorific value or heating value, the. Batteries capacity per volume or capacity per mass For example, the energy density of a lithium -polymer battery is 140-180 watt-hours per kilogram of mass ( 140-180 Wh / kg) and a nickel -metal hydride (NiMH) battery 80 Wh / kg. Compared with other types of electric energy storage of the battery cuts off pretty cheap.
What is desired is a high energy density in order to keep transport costs for the low energy, but also to achieve high operating durations of mobile devices and high ranges of vehicles. For example, can fly with a load of 80 grams for 5 minutes, a certain model helicopter when it draws its energy from an NiMH battery. With a lithium -polymer battery of the same mass, it remains twice as long in the air.
The energy density of an element is referred to as a physiological caloric value.
Examples
See also.
More energy densities
- Spectral power density: dependence of the energy of a radiation spectrum of the frequency.
- Acoustic energy density, the energy density of the sound field
- Calorific value (where the comparison of different energy densities of typical fuels )
- Specific or molar latent heat stored in the aggregate state energy
- Gravimetric energy density of food, used in the diet Volumetrics
- Shear energy density, the energy density at a shear