Physics, Techniques and ProceduresEnergy
fundamental physical quantity characterizing particles, waves and entire physical systems. In physics several types of energy are distinguished: gravitational and mechanical energy, electromagnetic energy, thermal energy,
nuclear energy and chemical energy. Energy is measured in
joule J , ergs, electron volts and, less frequently, in calories.
1 joule (J) = 1 kg m2/s2
1 erg= 1 g cm2/s2
1 electron volt (eV)= 1.6021892 10-19J
1 calorie (cal) = 4.1868 J
Energy is one of the quantities which in a closed physical system remains constant. This fundamental observation is termed the law of conservation of energy. In quantum theory energy is one of the quantities which may be quantized, as for example in the electronic energy levels of electrons in atoms hydrogen H .
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