Electric power (P) – the physical quantity characterizing action of electric current. It shows what work (on transfer of charged particles) is made by current per unit of time. In the International System of Units the power is expressed in watts, in honor of the English scientist James Uatt. (1vattt =1dzhoul/second).
Instruction
1. Any power is a speed of performance of work, so and electric - it is possible to calculate through work: É =. Proceeding from this formula, calculation of one Watt is visible: 1vattt = 1dzhoul/second. Knowing that electric work is on formula A = UIt/t, and substituting this expression in an initial formula of power, having performed simple mathematical operation, P=UI turns out. Example 1. It is necessary to find the power of the iron which is calculated on 220 Volts and works in network with current of 0.3 And. The solution of such task has an appearance: Р = UI = 220B*0,3A = 66 W.
2. It is possible to calculate electric power, considering the sizes given in Ohm's law for subcircuit. The law of Ohm says: I=U/R where U is tension of network, I - the current, R - resistance of the conductor. If instead of the current of I in a formula power of P=UI to substitute U/R, then it will turn out: P=U*U/R=U (in a square) / R. Example 2. Let it is necessary to find the power of the iron intended for network 220B which resistance of a spiral is equal 100 Ohms. Finding of power: P=U*U/R=220B*220B/100 of Ohms =484 W.
3. Other option physical sense. P = I*I*R=I (in a square) * R. Example 3. Let it is necessary to find the power of the device with a resistance of 16 Ohms, and A. Togd with a current of 1 R=1A*1A*16Om =16 W.