Power and time of use are the factors that determine how much energy is used by an electrical appliance or piece of equipment. Power is the rate at which energy is used, or work is done per unit of time. Electrical power is usually measured in watts; hence, electrical power is often referred to as wattage. The higher the wattage, the greater the amount of electrical energy that an electrical appliance or piece of equipment uses over a period of time. For example, a 1,200-watt microwave oven uses twice as much electrical energy and produces twice as much heat in one minute as a 600-watt microwave oven.
However, an appliance with a higher wattage will not use much energy if it is used for only a few seconds, whereas an appliance with a lower wattage may use a lot of energy if it is used for a number of hours. For instance, a 1,200-watt microwave used for only 30 seconds uses less energy than a 600-watt microwave does in one-half hour.
The relationship between the wattage, time of use, and the energy used by an appliance or piece of equipment can be expressed by this formula:
By using this formula, we can compare the energy used by electrical appliances and equipment to see which ones use the most electricity.
The information on the label tells us that the microwave oven needs 120 volts of electricity in the form of alternating current (AC) to operate and draws 5 amps (amperes) of current during its use. The 60 HZ number means that the current alternates at a rate of 60 times per second. The wattage of the microwave is 600 watts.
If the voltage and current are listed on an appliance but the wattage is not, the wattage can be calculated by multiplying the voltage by the current. Using the information on the microwave label, the wattage is equal to Voltage x Current = Wattage.
120 volts x 5 amps = 600 watts
If the microwave oven has used an average of a half hour each day, the average amount of energy it uses per day is
Wattage x Time = Energy Use
600 watts x 0.5 hours per day = 300 watt-hours per day
The relationship between voltage and electric current is similar to the relationship between the height of a waterfall and the water that flows down it. A height is needed for the water to flow down the waterfall. The greater the height of the waterfall, the more energy the water has when it reaches the bottom. If no height exists, the water will not flow, and it will not have any energy due to motion.
A voltage (similar to height) is needed to cause an electric current to flow (think of cascading water) so that it can deliver energy to an electrical device or appliance. It is helpful to remember that a current is a flow of electrons, and electrons have mass (therefore, current is a mass of flowing electrons!). The higher the voltage, the more work an electric current can do. If no voltage exists, a current will not flow, and work cannot be done.
The current produced by sources of electricity comes in two main forms: direct current (DC) and alternating current (AC).
In general, power is defined as the rate at which work is done, or energy is used per unit of time. Electric power specifically refers to the rate at which a source of electricity produces energy or refers to the rate at which an electrical device, appliance, or piece of equipment converts electrical energy into other forms of energy. The faster a source of electricity (such as a generator) produces electrical energy, the greater its power output. The faster an electrical device (such as a light bulb) converts electrical energy into light and heat energy, the greater its power consumption. Electric power is related to voltage and current by the following formula: Power = Voltage x Current
The unit of electrical power is the watt. One watt is defined as one joule (0.74 foot-pounds) per second or one volt multiplied by one amp. Because the watt unit is used so frequently, electrical power is often referred to as wattage.
…many of our small and medium appliances never stop using electricity! Experts call this usage “standby consumption” or “leaking electricity” because people are often not aware that the appliance is using electricity.