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Electrical Units and Metric Prefixes
A unit of measurement can be defined as a quantity chosen as a standard in terms of which other quantities may be expressed.
Engineering is an applied science dealing with a variety of physical quantities (a physical quantity is one which can be measured) like time, speed, voltage, resistance etc. Hence, for the measurement of these quantities standard units are defined.
There are a number of electrical units defined which are based on the SI system of units.
Standard Electrical Units of Measurement
| Electrical Quantity | Symbol for Quantity | Measuring Unit | Symbol for Unit |
|---|---|---|---|
| Charge | Q or q | Coulomb | C |
| Voltage | V or v | Volt | V |
| EMF | E or e | Volt | V |
| Current | I or i | Ampere | A |
| Resistance | R or r | Ohm | Ω |
| Inductance | L | Henry | H |
| Capacitance | C | Farad | F |
| Conductance | G | Mho or Siemen | ℧ or Ω-1or S |
| Power | P | Watt | W |
| Frequency | f | Hertz | Hz |
| Impedance | Z | Ohm | Ω |
Other Units for Electrical Measurement
| Electrical Quantity | Symbol for Quantity | Measuring Unit | Symbol for Unit |
|---|---|---|---|
| Electrical Energy | W or E | Watt – Hour | Wh |
| Phase Angle | θ | Degree or Radian | ° or Rad |
| Angular Frequency | ω | Radian/ Second | Rad/s |
| Time Period | T | Second | s |
| Time Constant | τ | Second | s |
Multiples and their Metric Prefixes
In electrical and electronics engineering, a wide range of values are encountered between maximum and minimum values of a standard electrical unit. Hence, when the quantities being measured are very large or very small, then multiples of the electrical measuring units are used by placing a prefix with the unit.
| Metric Prefix | Symbol | Multiplier | Power of Ten |
|---|---|---|---|
| yotta | Y | 1,000,000,000,000,000,000,000,000 | 1024 |
| zetta | Z | 1,000,000,000,000,000,000,000 | 1021 |
| exa | E | 1,000,000,000,000,000,000 | 1018 |
| peta | P | 1,000,000,000,000,000 | 1015 |
| tera | T | 1,000,000,000,000 | 1012 |
| giga | G | 1,000,000,000 | 109 |
| mega | M | 1,000,000 | 106 |
| kilo | k | 1000 | 103 |
| hecto | h | 100 | 102 |
| deca | da | 10 | 101 |
| deci | d | 1/10 | 10-1 |
| centi | c | 1/100 | 10-2 |
| milli | m | 1/1000 | 10-3 |
| micro | μ | 1/1,000,000 | 10-6 |
| nano | n | 1/1,000,000,000 | 10-9 |
| pico | p | 1/1,000,000,000,000 | 10-12 |
| femto | f | 1/1,000,000,000,000,000 | 10-15 |
| atto | a | 1/1,000,000,000,000,000,000 | 10-18 |
| zepto | z | 1/1,000,000,000,000,000,000,000 | 10-21 |
| yocto | y | 1/1,000,000,000,000,000,000,000,000 | 10-24 |
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