Page 207 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

Electrical power, energy and their units, calculation with assignments

Electric Power
In mechanical terms we defined power as the rate of doing work. The unit of power is Watt. In an electrical circuit
also the unit of electrical power is 1 Watt. In mechanical terms 1 Watt is the work done by a force of 1 N to move
the body through 1 metre in one second. In an electrical circuit, the electromotive force overcomes the resistance
and does work. The rate of doing work depends upon the current flowing in the circuit in amperes. When an e.m.f
of one volt causes a current of 1 ampere to flow the power is 1 Watt.
Hence Power = Voltage x Current
P= V x l
Power in Watts = Voltage in Volts x Current in Amperes

Electric work, energy
Electrical work or energy is the product of electrical power and time
Work in Watt seconds = Power in Watts x time in sec seconds
W = P x t

Since 1 joule represents 1 Watt x 1 sec, which is very small, larger units such as 1 Watt hour and 1 kilowatt hour
are used.
1 W.h = 3600 Watt sec.
1 Kwh = 1000 Wh = 3600000 Watt sec

Note: The charge for electric consumption is the energy cost per Kwh and it varies according to the
country and states.

V - Voltage (Volts) V

i - Current Intensity (Ampheres) A
P - Power (Watts, Kilowatts) W, kW
W - Work, Energy (Watt hour, Kilowatt hour) wh, Kwh
t - time (hours) h

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CITS : WCS - Electrical - Exercise 18