Like all other forms of energy, electrical energy is the capacity to do work. Like other forms of energy, electrical energy can be converted into other forms such as light energy, heat energy etc. Energy can only be transferred when a difference in energy level exists.
Energy and Power
Power is the rate at which energy is converted into another form. The power is measured in terms of Watts. If the amount of power is high, large amount of energy will converted in a given time. Joule is the unit of energy.1watt is equal to 1 joule per second. Thus power can be calculated as
P= J / t W. Thus 1 joule is 1 Watt x 1 second
Hence joule is measured in watt seconds. If the power is measured in kilo watts and time in hours, then the unit of electrical energy is kilo-watt hour or kWh. Electricity tariff is based on kWh.
Energy consumption of appliances can be easily calculated. For example, if a computer rated 200 Watts is running 60 minutes, then the energy consumption will be
J = Pt
P is the power rating of computer – 200 W
t is the time in seconds. That is 60 minutes x 60 = 3600 seconds
Thus energy consumption J is 200 x 3600 = 720000 J or 720 kilo Joule
Electric energy form
AC power is graphically represented as Sine wave or Sinusoidal wave. It has two alternating cycles and one cycle is one complete repetition of the sine wave pattern. The domestic electric supply has 50 cycles and hence 50Hz. In some counties it is 60Hz.
The important features of AC power are Amplitude, Cycles, Frequency, Peak-to-Peak, and RMS.
Amplitude is the maximum value of current or voltage. It is represented by either of the two “peaks” of the sine wave. This maximum voltage level is also called as t “Peak Voltage”. It can be either positive or negative. Positive and negative refers to the direction of current flow. A negative number does not mean that the voltage is Zero but it represents the current flows in the opposite direction.
In the Sine wave, one cycle is the one complete repetition of the sine wave pattern. The sine wave begins from zero, goes to positive through the Positive Peak, then to negative through zero, reaches the Negative Peak and to the zero.
Frequency is the number of times the Sine Wave Pattern Cycle occurs in a second. The unit of measurement for Frequency is Hertz. The name is given in honor of the scientist Heinrich Rudolf Hertz.
4. Peak-to- Peak voltage
Peak-to-peak voltage is the voltage measured between the maximum Positive and Negative Amplitudes on the sine wave. Its value is twice that of Amplitude. Peak to peak voltage is the maximum voltage available. But this voltage not all usable in practical applications.
5. Root mean square – r.m.s
RMS value is the effective or usable value of a varying voltage or current.RMS is the standard way of measuring and reporting effective Alternating Current and voltage. It is not the peak voltage but the average voltage available. The RMS value can be determined by
The RMS is found by multiplying the Peak Amplitude by the Square Root of 2.That is approximately 0.707. RMS voltage (VRMS) is 0.707 or about 71% of the peak voltage (VPEAK).The domestic electricity is rated at 230 volt r.m.s. Hence the peak voltage is
Peak = 230 x 1.414 = 325 volts
The peak voltage is the maximum value present in a varying alternating voltage. That is from 0V to maximum positive voltage.
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