Electrical Engineering ⇒ Topic : Electric Power
The rate at which work is done in an electric circuit is called its electric power i. e.
When voltage is applied to a circuit, it causes current (i.e. electrons) to flow through it. Clearly,work is being done in moving the electrons in the circuit. This work done in moving the electrons in a unit time is called the electric power. Thus referring to the part AB of the circuit [See Fig. (a)]
V = P.D. across AB in volts
I = Current in amperes
R = Resistance of AB in Ω.
t = Time in sec. for which current flows
The total charge that flows in t seconds is Q=I x t coulombs and by definition (See Art. a),
The above three formulae are equally valid for calculation of electric power in a d.c. circuit. Which one is to be used depends simply on which quantities are known or most easily determined
Unit of electric power. The basic unit of electric power is joules/sec or watt. The powerconsumed in a circuit is 1 watt if a p.d. of 1 V causes 1 A current to flow through the circuit.
Power in watts = Voltage in volts x Current in amperes
The bigger units of electric power are kilowatts (kW) and megawatts (MW).
1 kW = 1000 watts ; 1 MW = 106 watts or 103 kW
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