How is Electrical Power Measured – the Watt, Joule, and kWh

Electric power is measured in watts, one of which is equal to one joule of work per second. Here, it becomes important to understand the difference, or relationship, between power and work. Power is defined as the rate at which “work” is done, or energy is converted. Energy can be delivered slowly, or quickly – depending on which it is, you’ll get less or more “power”.

Why? Because power is the rate of energy delivered per unit time, not the total energy. Work on the other hand, is defined as the force times the distance through which it acts. Correspondingly, the joule, common commercial electricity meterwhich is the SI unit of work, is equal to the force of one newton acting over a distance of one meter. Now let’s talk about practical applications.

The standard billing unit for electrical power in residential applications is the kilowatt-hour, or kWh. It is a unit of energy equal to 1000 watts used over a period of one hour. Here in Japan, it costs the equivalent of 25 to 30 cents per kilowatt-hour. It will most likely differ, even substantially, depending on region and country, but it gives you a ball-park figure.

All electrical appliances should have labels indicating their wattage, and by doing a calculation based on your local cost-per-kWh, it should give you a pretty good idea of what any one appliance is costing you. You can also incorporate this logic when you purchase new appliances, as newer technology often has lower power ratings for the same or higher performance.

The concept of investing in new electronic appliances with the idea of making monthly savings on your utility bills that will eventually surpass the initial cost of purchase, is certainly worth considering in this new era of ever-increasing electronic efficiency. Energy-efficient, or “eco-friendly” purchases that replace appliances that have long work-cycles, such as an air-conditioner, heater, or fridge, will naturally make the biggest difference.

  • Note that not all new electronic appliances will be more energy efficient by virtue of their “newness” alone. Certain manufacturers will invest more into this aspect than others. Stores will often capitalize on energy-efficient products by making the economic and ecological advantages clear without you having to even search them out.

In today’s modern world, it’s pretty safe to say that the convenience of our lives depend heavily on power. More specifically, on electric power. Electric power provides the bulk of the power we rely on in our households, which in turn translates Chart displaying world energy usageinto the power that most people are familiar with – or should be familiar with.

One thing to keep in mind is that electricity is power that must be generated by another source of energy, such as fossil fuels, hydropower, and nuclear power. This means that electricity is not really all that “clean” a form of energy due to the process with which it’s generated. This is the part that many people don’t realize and that power companies don’t tell you.

Back in the late 1930s when nuclear power was first being considered as a viable source of commercial energy, it was speculated that energy would become so cheap and plentiful that it would be “too cheap to meter”. This of course, hasn’t happened yet. Today, 80 years and dozens of nuclear power-related accidents later, we still wage war on the frontier of clean, renewable energy.

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