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Illustration of the "reference directions" of the current (), voltage (), and power () variables used in the passive sign convention.If positive current is defined as flowing into the device terminal which is defined to be positive voltage, then positive power (big arrow) given by the equation = represents electric power flowing into the device, and negative power represents power flowing out.
The negative-energy particle then crosses the event horizon into the black hole, with the law of conservation of energy requiring that an equal amount of positive energy should escape. In the Penrose process , a body divides in two, with one half gaining negative energy and falling in, while the other half gains an equal amount of positive ...
Power is the rate with respect to time at which work is done; it is the time derivative of work: =, where P is power, W is work, and t is time.. We will now show that the mechanical power generated by a force F on a body moving at the velocity v can be expressed as the product: = =
Higher potentials on the sphere can also be achieved by using a voltage source to charge the belt directly, rather than relying solely on the triboelectric effect. A Van de Graaff generator terminal does not need to be sphere-shaped to work, and in fact, the optimum shape is a sphere with an inward curve around the hole where the belt enters.
The mechanical power needed to assist in this production is provided by a number of different sources. These sources are called prime movers, and include diesel, petrol and natural gas engines. Coal, oil, natural gas, biomass and nuclear energy are energy sources that are used to heat water to produce super-heated steam. Non-mechanical prime ...
However, electromotive force itself is not a physical force, [5] and ISO/IEC standards have deprecated the term in favor of source voltage or source tension instead (denoted ). [ 6 ] [ 7 ] An electronic–hydraulic analogy may view emf as the mechanical work done to water by a pump , which results in a pressure difference (analogous to voltage) .
Faraday's law is a single equation describing two different phenomena: the motional emf generated by a magnetic force on a moving wire (see the Lorentz force), and the transformer emf generated by an electric force due to a changing magnetic field (described by the Maxwell–Faraday equation).
The energy source harnessed to turn the generator varies widely. Most power stations in the world burn fossil fuels such as coal , oil , and natural gas to generate electricity. Cleaner sources include nuclear power , and increasingly use renewables such as the sun , wind , waves and running water .