Electrical units of measurement encompass a range of quantities that are crucial for understanding and working with electrical and electronics systems. These units include basic and derived quantities such as voltage, current, resistance, power, and energy.
Here, we’ll provide a table listing common electrical units along with their symbols and brief explanations. Additionally, we’ll cover multiples and sub-multiples of these units using standard metric prefixes.
Common Electrical Units of Measurement
| Quantity | Unit | Symbol | Explanation |
|---|---|---|---|
| Voltage | Volt | V | Measure of electric potential difference. V = I × R |
| Current | Ampere | A | Measure of electric charge flow. I = V ÷ R |
| Resistance | Ohm | Ω | Measure of opposition to current flow. R = V ÷ I |
| Power | Watt | W | Measure of electrical power. P = V × I or I2 × R |
| Energy | Joule | J | Measure of energy (also kWh for electrical energy) |
| Capacitance | Farad | F | Measure of a capacitor’s ability to store charge. |
| Inductance | Henry | H | Measure of a coil’s ability to induce voltage. |
| Conductance | Siemens | G or | Measure of ease of current flow (inverse of resistance). |
| Charge | Coulomb | C | Measure of electric charge. |
| Frequency | Hertz | Hz | Measure of cycles per second. |
| Magnetic Flux Density | Weber | φ | Measure of magnetic field density. |
Multiples and Sub-Multiples Units
Electrical quantities often span a wide range of magnitudes, necessitating the use of multiples and sub-multiples. These are represented using standard metric prefixes.
Metric Prefixes
| Prefix | Symbol | Factor | Example |
|---|---|---|---|
| Tera | T | 1012 | 1 Tera-ohm (TΩ) = 1012 Ω |
| Giga | G | 109 | 1 Gigawatt (GW) = 109 W |
| Mega | M | 106 | 1 Megavolt (MV) = 106 V |
| Kilo | k | 103 | 1 Kilovolt (kV) = 103 V |
| Hecto | h | 102 | 1 Hectowatt (hW) = 102 W |
| Deca | da | 101 | 1 Decaampere (daA) = 101 A |
| (none) | (none) | 100 | 1 Volt (V) = 100 V |
| Deci | d | 10-1 | 1 Decivolt (dV) = 10-1 V |
| Centi | c | 10-2 | 1 Centiampere (cA) = 10-2 A |
| Milli | m | 10-3 | 1 Millivolt (mV) = 10-3 V |
| Micro | µ | 10-6 | 1 Microfarad (µF) = 10-6 F |
| Nano | n | 10-9 | 1 Nanowatt (nW) = 10-9 W |
| Pico | p | 10-12 | 1 Picofarad (pF) = 10-12 F |
| Femto | f | 10-15 | 1 Femtovolt (fV) = 10-15 V |
| Atto | a | 10-18 | 1 Attoampere (aA) = 10-18 A |
| Zepto | z | 10-21 | 1 Zeptowatt (zW) = 10-21 W |
| Yocto | y | 10-24 | 1 Yoctocoulomb (yC) = 10-24 C |
Examples of Using Multiples and Sub-Multiples.
Voltage:
- 1 kilovolt (kV) = (103) volts (V)
- 1 millivolt (mV) = (10-3) volts (V)
- Current:
- 1 Megaampere (MA) = (106) amperes (A)
- 1 microampere (µA) = (10-6) amperes (A)
- Power:
- 1 gigawatt (GW) = (109) watts (W)
- 1 nanowatt (nW) = (10-9) watts (W)
- Capacitance:
- 1 microfarad (µF) = (10-6) farads (F)
- 1 picofarad (pF) = (10-12) farads (F)
The decibel (dB) is a logarithmic unit used to express the ratio of two values, typically power or intensity. It is one-tenth of a bel, a unit named after Alexander Graham Bell. A power gain of 10 times corresponds to 10log10(10)=10 dB. Widely used in acoustics to measure sound levels.
The phase angle (θ) is the measure of the phase difference between two sinusoidal waveforms, such as voltage and current in an AC circuit. It indicates how much one wave is leading or lagging behind another.
The phase angle is measured in degrees (°) or radians (rad). In a purely inductive or capacitive circuit, the phase angle is ±90°.
Angular frequency (ω) is a measure of how rapidly an object rotates or oscillates. In the context of electrical circuits, it describes the rate of oscillation of a sinusoidal waveform. Crucial in the study of alternating current (AC) circuits and electromagnetic waves.
For a standard 60 Hz AC power supply, the angular frequency is ω = 2π × 60 ≈ 377 rad/s.
Summary
Understanding the various units of electrical measurement and their multiples and sub-multiples is essential for working effectively in the field of electrical engineering and related disciplines. The use of standard metric prefixes simplifies the handling of extremely large or small values, making calculations and communication more manageable.