In use the joule and kilojoule are common, with larger multiples seen in limited contexts. The SI unit of power is the watt, one joule per second. The watt second is a unit of energy, equal to the joule. SMA actuators are typically actuated electrically by Joule heating. Energy released is measured in Joule per mole. A heating element converts electrical energy into heat through the process of Joule heating. This explains the physical significance of the name "joule per radian". SMA actuators are typically actuated electrically, where an electric current results in Joule heating. The eddy currents flowing through the resistance of the material heat it by Joule heating. Airsoft guns and pistols are allowed a muzzle energy equal or minor to one joule. This is the phenomenon of electrical resistance and Joule heating. As energy, its SI unit is the joule (J). The phenomenon was first studied by James Prescott Joule in 1841. The SI unit for energy is the joule (J). This is known as the Joule effect.