Still many think that power is the same, as tension, current or energy, or believe that the electric device is larger, the it is more powerful. But whether so it actually? Let's find out.
Power is called the amount of energy which is marked out or spent by any given object per unit of time. In the SI system unit of quantity of energy is the joule, and unit of time - second therefore it is logical that the power unit has to be equal to one joule a second in this system. Such unit is called watt (W), in honor of the Scottish scientist and the inventor James Uatt (1736-1819). The device for measurement of power carries the name of a wattmeter. In electrical equipment the power is calculated by multiplication of current by tension. That it turned out in watts, it is necessary that tension was expressed in volts, and current - in amperes. Units any from watt - picowatt, microwatt, milliwatt, kilowatt, megawatt, terawatt and others. At change of tension the current through loading which resistance is invariable changes under the linear law, and the power allocated on it - on square.
But, certainly, also the devices which are not electric can have any given power. All of them develop or absorb any given amount of energy per unit of time. But in case energy is mechanical, quite often apply other, stand-alone unit - horsepower. Despite the name, it is power unit, but not forces. In English it is called horsepower that is literally translated as horse power. There are several standards on horsepower, on the most widespread of them it is equal to 735.49875 W.
Knowing device power, it is possible to calculate what amount of energy it will consume per unit of time. But in joules it is inconvenient to express this energy therefore usually for this purpose apply one more stand-alone unit - kilowatt-hour. In these units the ordinary electric meter counts energy. The gross blunder is the popular belief as if the 50-90 W device (consumes the ordinary laptop so much) will spend for an hour energy in 50-90 kilowatt-hours. Under this pretext the parents quite often forbid children to use the computer too long. Actually, 50-90 W are only 0.05-0.09 kW. And of course, the power consumed by the device does not depend on its size at all. The color TV and the fridge, having considerable dimensions, even working at the same time, consume the smaller power, than the iron or the hair dryer, rather small by the sizes, by five-ten times. And the power of the car is approximately a hundred times more than the same parameter of the iron.