Pneumatic circuit following devices operate using compressed gases, but are not normally thought of as being pneumatic circuits: Pneumatic circuit A pneumatic circuit is an interconnected set of components that convert compressed gas (usually air) into mechanical work. In the normal sense of the term, the circuit must include a compressor or compressor-fed tank. The circuit comprises the following components: In general, based on the application, a pneumatic cylinder is usually a single acting cylinder, where there is a single port in the cylinder and where cylinder extension is done by compressed air and retraction by means of open coiled spring. In
Electric potential energy time-invariant electric fields. The electric potential energy of a system of point charges is defined as the work required assembling this system of charges by bringing them close together, as in the system from an infinite distance. ^\mathbf{r} q\mathbf{E}(\mathbf{r'}) \cdot \mathrm{d} \mathbf{r'}</math>, The electrostatic potential energy can also be defined from the electric potential as follows: The SI unit of electric potential energy is the joule (named after the English physicist James Prescott Joule). In the CGS system the erg is the unit of energy, being equal to 10 J. Also electronvolts may be used, 1 eV = 1.602×10 J.