the mechanical advantage These relations are important because they define the maximum performance of a device in terms of velocity ratios determined by its physical dimensions. See for example gear ratios. Electrical power The instantaneous electrical power P delivered to a component is given by where is the instantaneous power, measured in watts (joules per second) is the potential difference (or voltage drop) across the component, measured in volts is the current through it, measured in amperes If the component is a resistor with time-invariant voltage to current ratio, then: where is the electrical resistance, measured in ohms. Peak power and duty cycle In the case of a periodic signal of period , like a train of identical pulses, the instantaneous power is also a periodic function of period . The peak power is simply defined by: The peak power is not always readily measurable, however, and the measurement of the average power is more commonly performed by an instrument. If one defines the energy per pulse as: then the average power is: One may define the pulse length such that so that the ratios are equal. These ratios are called the duty cycle of the pulse train. Radiant power Power is related to intensity at a radius ; the power emitted by a source can be written as: See also Simple machines Orders of magnitude (power) Pulsed power Intensity – in the radiative sense, power per area Power gain – for linear, two-port networks Power density Signal strength Sound power References Force Temporal rates Physical quantities