Measuring Electricity
Electricity can be measured in a variety of ways, including watts, volts, ohms, and amperes. Each of these measurements applies to a certain aspect or quality of electricity. Each are important in describing electricity.
Watts, Kilowatts, and Megawatts
In the electricity industry, units of electric power are expressed as watts. How are electricity and power different from each other? Electricity is a form of energy and is the movement of electrons along a circuit. Power is a measure of the use of electricity, or any other form of energy, in terms of work over a time interval.
Watts can refer either to power generated or consumed. Common references include electricity generated by a wind turbine or solar panels,and the electricity consumed by a lamp or household appliance. Watts measure total electrical power based on the variables of volt, amperes (amps), and ohms.
One watt is equal to the rate of current flow when 1 volt moves 1 ampere (6.25 x 1018 electrons per second) through a circuit. This is also equal to one joule/second.
- 1,000 watts equals 1 kilowatt (kW); which is the approximate amount an average American home consumes at any given time
- 1,000 kW equals 1 megawatt (MW); which is the approximate amount consumed by 1,000 homes
Electricity use is measured by watt-hours (Wh), kilowatt-hours (kWh), or megawatt-hours (mWh) and is calculated by multiplying the watts required by the number of hours used.
For example: A 60-watt light bulb used for 5 hours requires 300 watt-hours of electricity. A typical home in Massachusetts uses 600 kilowatt-hours of electricity each month.
Volts
Voltage can be compared to the pressure of water in a hose. The higher the pressure, the faster the water will flow through the hose. Similarly, the higher the voltage of the electricity, the faster it will flow from a source of electricity to an end use.
A volt, or the unit of voltage, is a common electrical measurement. It is used, for example, to discuss the transmission of electricity from power plants to end users. Utilities distinguish their transmission lines by voltage, with high voltage transmission lines bringing large amounts of power to local lines which have lower voltage.
Ohms
Ohms measure resistance and can be compared to the diameter measurement of a hose. A smaller diameter hose will allow less water to flow through than a larger diameter hose. Similarly, a thinner wire increases resistance, causing a lesser amount of electricity to be transmitted because it is encountering resistance in the wire. To reduce resistance, certain metals are used to conduct electricity, such as copper, which allows electrons to flow easily.
Amperes
Amps can be compared to the volume of water that flows through a hose. The volume of water that flows past a certain point in a specific amount of time can be measured. Similarly, amps measure the number of electrons that pass a specific point within a certain amount of time (rate of current) in a circuit. One ampere is equivalent to approximately 6.25 x 1018 electrons passing by a specific point in one second. The rate of the electric current is dependent upon the voltage and resistance. A circuit with high voltage and low resistance will have more amps (greater number of electrons passing through the circuit) than a circuit with low voltage and higher resistance. The former example has more power than the latter. The amount of amps in a circuit is important to measure because it can help calculate the amount of power consumption/output of a circuit.