Beatrice Lang
The basic units of electricity are current, voltage, and resistance. Current, measured in amps, is the rate at which charge is flowing—how fast the electrons are moving. Voltage, measured in volts, is the force or pressure with which electricity moves through a circuit. Resistance, measured in ohms, is a material's tendency to resist the flow of charge (current). Power, measured in watts, is the rate at which energy is used or transferred. These electrical units of measurement are based on the International System of Units (SI).
| Characteristics | Values |
|---|---|
| Standard unit of electricity | Defined systematically, starting with the ampere, which comes from the charge and coulomb of an electron |
| SI units | Volt (V) for voltage, Ohm (Ω) for resistance, and Ampere (A) for current |
| Range | Minimum and maximum values exist for standard electric units, e.g., resistance can range from 0.001 ohms to 100,000 ohms |
| Watt-Hour (Wh) | Measures the amount of electric energy consumed by a circuit over time, e.g., a bulb consumes 100 watts per hour |
| Decibel (dB) | Represents a gain in voltage, power, or current and is one-tenth of a Bel (B) |
| Phase Angle (θ) | Difference in degrees between voltage and current waveforms with the same time period, measured in radians |
| Angular Frequency (ω) | Used in AC circuits to represent the phase relation between two waveforms |
| Time Constant (τ) | Characteristic of an impedance circuit, representing time for output to reach 63.7% of its minimum or maximum |
| Basic units | Volts, Amps, Ohms, and Watts |
| Voltage (V) | Represents force or pressure of electricity in a circuit |
| Current (amperes, A) | Indicates the amount of electric current flowing through a conductor |
| Power (Watts, W) | Calculated by multiplying volts by amperes (P = V x A) |
| Kilowatt-hours (kWh) | Used to measure active energy |
| Reactive energy | Measured in kilovolt-ampere reactive hours (kVArh) |
| Active power | Measured in kilowatts (kW), it is the useful work done by electricity to power devices |
| Reactive power | Measured in kilowatt-reactive (kVAR), it is necessary for maintaining voltage in circuits |
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What You'll Learn
- Volts (V) measure voltage, the force of electricity moving through a circuit
- Amps (A) measure current, or how fast electrons are moving
- Ohms (Ω) measure resistance, a material's tendency to resist electric current
- Watts (W) measure power, or the rate at which energy is transferred
- Kilowatt-hours (kWh) measure active energy, the energy used to power devices
Volts (V) measure voltage, the force of electricity moving through a circuit
Volts (V) are the unit of measurement for voltage, which is the force of electricity moving through a circuit. Voltage is a fundamental concept for understanding how electricity flows in our devices and homes. It is the pressure from an electrical circuit's power source that pushes charged electrons (current) through a conducting loop, enabling them to do work such as illuminating a light.
The volt is a measure of electric potential, which is distinct from force or energy consumption. It is analogous to lifting a rock in a gravity field—the higher the rock is lifted, the more energy has been used. In the case of electricity, voltage is the measure of how "far" a charge has been "lifted" in an electric field.
The volt is defined as the energy consumption of one joule per electric charge of one coulomb. One joule is the amount of work required to make a watt of power for a second, or to move a body one meter with a one-Newton force. In the International System of Units (SI), the derived unit for voltage is the volt.
The hydraulic analogy is a useful way to understand voltage. In a hydraulic system, the work done to move water is equal to the pressure drop multiplied by the volume of water moved. Similarly, in an electrical circuit, the work done to move electrons is equal to the electrical pressure difference multiplied by the quantity of electrical charges moved. The larger the pressure difference between two points, the greater the flow of electricity between them.
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Amps (A) measure current, or how fast electrons are moving
The ampere, or amp, is a standard unit of electrical measurement for electric current. Amperage is the rate at which current is flowing through a circuit or the number of electrons moving through a wire. In other words, it measures how fast electrons are moving.
The amp was named after French physicist André-Marie Ampère, who laid the foundation of electrodynamics and made significant contributions to the creation of modern electrical science. Ampère's force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere.
The SI unit of charge, the coulomb, is defined as "the quantity of electricity carried in 1 second by a current of 1 ampere". In other words, a current of one ampere is one coulomb of charge passing through a point per second.
Amperage is listed in units of amps (or amperes). In a home's service panel or breaker box, you might see different circuit breakers listed as 15 amps, 20 amps, or 30 amps. The larger the amperage, the more electricity can flow through the circuit.
The relationship between voltage, amperage, and wattage can be expressed by the equation V x A = W, where V is voltage, A is amperage, and W is wattage. This equation shows that the faster each electron moves through a circuit, and the greater the volume the circuit can hold, the higher the wattage.
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Ohms (Ω) measure resistance, a material's tendency to resist electric current
Ohms (Ω) are the standard unit of electrical resistance in the International System of Units (SI). They are used to measure how much a material resists the flow of electric current. This is known as electrical resistance.
The ohm is named after German physicist Georg Ohm (1789-1854), who introduced Ohm's Law. This states that there is a proportional relationship between voltage, current, and resistance in an electrical circuit. In simpler terms, ohms can be described as the equivalent of one volt per one ampere (V/A).
The ohm is defined as the electrical resistance between two points of a conductor when a constant potential difference of one volt (V) is applied to those points and a current of one ampere (A) is produced. The formula for this is: voltage = current x resistance, or V = I x R.
The resistance of a material depends largely on the material itself. For example, materials made of electrical insulators like rubber tend to have very high resistance, whereas materials made of electrical conductors like metals tend to have very low resistance. However, the size and shape of an object also play a role in resistance, as these properties are extensive rather than intensive.
Ohms can be expressed in larger or smaller quantities, depending on the amount being measured. For example, one megaohm is equal to 1,000,000 ohms, whereas a microohm is 0.000001 of a single ohm.
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Watts (W) measure power, or the rate at which energy is transferred
The watt (W) is the standard unit of power in the International System of Units (SI). It is used to quantify the rate of energy transfer, or the rate at which energy is generated or consumed. In other words, watts measure how fast energy is being used.
In electrical systems, power is calculated by multiplying volts (a measure of the force or pressure with which electricity moves through a circuit) by amperes (a measure of the amount of electric current flowing through a conductor). So, in terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V). This is equivalent to the volt-ampere.
The watt was named after James Watt, the 18th-century Scottish inventor who improved the Newcomen engine with his own steam engine in 1776. His invention was fundamental to the Industrial Revolution.
In practice, watts are used to measure the power of radio transmitters, power stations, and electrical appliances. For example, a typical lightbulb consumes 100 watts of power per hour, while a medium-sized car might consume 100,000 watts.
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Kilowatt-hours (kWh) measure active energy, the energy used to power devices
Kilowatt-hours (kWh) are a measure of energy usage over time. A kilowatt (kW) is a measure of how much power something needs to run. One kilowatt is equal to 1,000 watts. So, a kilowatt-hour is the amount of energy consumed by a device that uses 1,000 watts of power in an hour.
For example, a 100-watt lightbulb would need 10 hours to consume 1 kWh, while an oven would consume the same amount in about 30 minutes. A kWh is a useful unit of measurement because it standardizes energy usage, allowing for easy comparisons between different devices and systems.
The average home in the United States consumes approximately 900 kWh of electricity each month, with an average annual consumption of around 10,800 kWh. This can vary depending on the size of the home, the efficiency of appliances, the time of year, and individual energy habits.
To calculate the kWh rate you pay for electricity, you can divide your total utility bill (excluding flat fees and taxes) by your total power consumption. This rate may also be displayed directly on your electricity bill.
It's important to note that while "kilowatt-hours" and "kilowatts" both use the "kW" abbreviation, they are different units. Kilowatts measure the amount of power needed to turn a device on, while kilowatt-hours measure the amount of energy used by that device over time.
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Frequently asked questions
The standard units of electrical measurement for voltage, current, and resistance are Volt (V), Ampere (A), and Ohm (Ω) respectively.
Watt is the basic unit of electric, mechanical, or thermal power. One Watt is equal to one Ampere under the pressure of one Volt. Watts can be calculated by multiplying Volts by Amperes.
Power is measured in Watts.
Energy is measured in Watt-Hours (Wh) or Kilowatt-Hours (kWh).
