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Letter To The Editor: Proper Use Of Units In Electrical Matters ... Does Matter

on August 12, 2017 - 6:38am
Chief Technical Officer, Ph.D.
Antenna Development Corporation
Las Cruces
Perhaps I am too concerned with the proper use of units in electrical matters. Here is a short tutorial (perhaps of interest to Andy Andrews link):
  • We pay for electricity in units of kWh - that is, the integrated product of the power consumption times the length of time. For example, a 1 kW load uses an energy of 1 kWh. Reduced to the basic terms of electrical energy, the number of Joules (energy). The equations of physics and engineering very carefully state the units to, among other things, enable the precise comparison of energy consumption, power, and efficiency between various options.
  • A gallon of gasoline does not have 32.78 kW of energy - the number written is a power number - not an energy number. It stands for 32.78 times 1000 Joules per second. Conversion of power to energy requires the multiplication of the power and time. It may be that a gallon of gasoline has 32.78 kWh of energy - I did not check. By the way, why do I use the strange capitalization's? k = kilowatt = lower case. W = Watt = the name of James Watt = capitalized because it refers to James Watt. J = Joule - because it references James Prescott Joule. It is important to use the proper capitalization in physics and engineering to prevent confusion.
  • To be accurate, a light bulb does not consume 60 Watts per hour. Rather, a 60 Watt light bulb consumes power at the rate of 60 Joules per second and in an hour it consumes a total of 0.06 kWh of energy. So when you look at the power meter on your house, it will advance by 0.060 kWh after an hour of use of the 60 W light bulb.
While the conclusions of Mr. Andrews may be correct, the units and the calculations are garbled by the improper use of the “units” in the equations. Hopefully the editors and Mr. Andrews may be able to make sure that articles use the proper units of engineering.