Engineering Quantities
and
International Standard of Units
The International System of Units (abbreviated SI from French- Le Système international unit's) is the modern form of the metric system and is the world's most widely used system of measurement, used in both daily commerce and science. It comprises a coherent system of units of measurement built around seven base units, 22 named and an indeterminate number of unnamed coherent derived units, and a set of prefixes that act as decimal-based multipliers. It's part of the International System of Quantities.
Base units
Units of measurement list are the building blocks of SI and all other units of measure can be derived from the base units.
International System of Units
| Unit name | Unit symbol | Quantity name | Usual symbol |
|---|---|---|---|
| Metre | m | Length | L |
| Kilogram | kg | Mass | M |
| Second | s | Time | T |
| Ampere | A | Electric current | I |
| kelvin | K | Thermodynamic temp. | Θ |
| Mole | mol | Amount of substance | N |
| Candela | cd | Luminous intensity |
 |
| BASIC UNITS |
SI unit of measurement
| Unit name | Unit symbol | Quantity name | Usual symbol |
|---|---|---|---|
| volt | V | Voltage | V |
| amp* | A | Current | I |
| coulomb | C | Charge | Q |
| ohm | Ω | Resistance | R |
| farad | F | Capacitance | C |
| henry | H | Inductance | L |
| ohm | Ω | Reactance | X |
| ohm | Ω | Impedance | Z |
| watt | w | Power | P |
| joule | j | Energy | E |
| second | s | Time | t |
| hertz | Hz | Frequency | f |
Quantities and Units in Electrical and Electronics
Volt (V or E):
Volt is the electrical unit of voltage. Measuring unit of volt is represented by a letter V or E.
One volt is the energy of 1 joule that is consumed when electric charge of 1 coulomb flows in the circuit.
One volt is the energy of 1 joule that is consumed when electric charge of 1 coulomb flows in the circuit.
वोल्ट वोल्टेज की विद्युत इकाई है। वोल्ट की मापने की इकाई को V या E अक्षर से दर्शाया जाता है।
एक वोल्ट 1 जूल की ऊर्जा है जो परिपथ में 1 कूलॉम का विद्युत आवेश प्रवाहित करने पर खपत होती है।
1V = 1J / 1C
Ampere (A):
Ampere is the electrical unit of electric current. Measuring unit of ampere is represented by a letter I or i. It measures the amount of electric charge that flows in an electrical circuit per 1 second.
1A = 1C / 1s
Ohm (Ω):
Ohm is the electrical unit of resistance. Measuring unit of Ohm is symbolized by a latter R or a Greek letter Ω. For AC the resistance is said Impedance and is represented by a letter Z.
ओम प्रतिरोध की विद्युत इकाई है। ओम की मापने की इकाई को बाद वाले आर या ग्रीक अक्षर Ω द्वारा दर्शाया गया है। एसी के लिए प्रतिरोध को प्रतिबाधा कहा जाता है और इसे एक अक्षर Z द्वारा दर्शाया जाता है।
1Ω = 1V / 1A
Z [Ω] =√ (R2+X2)
Watt (W):
Watt is the electrical unit of electric power. It measures the rate of consumed energy.
वाट विद्युत शक्ति की विद्युत इकाई है। यह खपत ऊर्जा की दर को मापता है।
1W = 1J / 1s1W = 1V • 1A
Decibel-milliwatt (dBm):
Decibel-milliwatt or dBm is a unit of electric power, measured with logarithmic scale referenced to 1mW.
10dBm = 10 •log10 (10mW / 1mW)
Decibel-Watt (dBW):
Decibel - watt or dBW is a unit of electric power, measured with logarithmic scale referenced to 1W.
डेसीबल-वाट या डीबीडब्ल्यू विद्युत शक्ति की एक इकाई है, जिसे 1W के संदर्भ में लघुगणकीय पैमाने से मापा जाता है।
10dBW = 10 • log10(10W / 1W)
Farad (F):
Farad is the unit of capacitance. Measuring unit is represented by a letter C. It represents the amount of electric charge in coulombs that is stored per 1 volt.
फैराड समाई की इकाई है। मापने की इकाई को एक अक्षर C द्वारा दर्शाया जाता है। यह कूलम्ब में विद्युत आवेश की मात्रा को दर्शाता है जो प्रति 1 वोल्ट संग्रहीत होता है।
1F = 1C / 1V
Henry (H):
Henry is the unit of inductance. Measuring unit symbol is represented by a letter H or L.
1H = 1Wb / 1A
Siemens (S):
Siemens is the unit of conductance, which is the opposite of resistance. The measuring unit of conductance is represented by a letter G
1S = 1 / 1Ω=1Mho
Coulomb (C):
Coulomb is the unit of electric charge.
1C = 6.238792×1018 electron charges
Ampere-hour (Ah):
Ampere - hour is a unit of electric charge. One ampere-hour is the electric charge that flow in electrical circuit, when a current of 1 ampere is applied for 1 hour.
एम्पीयर-घंटा विद्युत आवेश की एक इकाई है। एक एम्पीयर-घंटा वह विद्युत आवेश होता है जो विद्युत परिपथ में प्रवाहित होता है, जब 1 एम्पीयर का करंट 1 घंटे के लिए लगाया जाता है।
1Ah = 1A • 1hour
One ampere-hour is equal to 3600 coulombs.
1Ah = 3600C
Tesla (T):
Tesla is the unit of magnetic field.
1T = 1Wb / 1m2
Weber (Wb):
Weber is the unit of magnetic flux.
1Wb = 1V • 1s
Joule (J):
Joule is the unit of energy.
1J = 1 kg • 1(m / s)2
Kilowatt-hour (kWh):
Kilowatt-hour is a unit of energy.
1kWh = 1kW • 1h = 1000W • 1h
Kilovolt-amps (kVA):
Kilovolt-amps is a unit of apparent power.
1kVA = 1kV • 1A = 1000 • 1V • 1A
Hertz (Hz):
Hertz is the unit of frequency. It measures the number of cycles per second.
1 Hz = 1 cycles / s
Volt-Ampere-Reactive (Var):
Var is the unit of Reactive power and its measuring unit symbol is represented by a letter Q. In inductor or capacitor how much magnetic or electric field made by 1Ax1V is called the unit of reactive power.
1Var=1V•1A
Q= V•I •sinθ; This can be positive for inductance and negative for capacitance.
Ohm-meter (Ω·m):
Ohm-meter is the unit of electrical Resistivity. Resistivity is symbolized by Greek small letter
Rho “ρ”.
1 Ω•m=1Ω•1m
Siemens per meter (S/m):
Siemens per meter is the unit of Conductivity. Measuring unit of conductivity is represented by Greek small letter sigma “σ”
1S/m=1siemence/1meter
Volts per meter (V/m):
Volts per meter is the unit of Electric Field. Measuring unit of Electric Field is symbolized by a letter E.
1V/m=1Volt/1meter
Newton per coulomb (N/C):
Newton per coulomb is the unit of Electric field. The unit of measuring of Electric Field is symbolized by a letter “E”.
1N/C=1Newton/1Coulomb
Volt-meter (V·m):
Volt-meter is the unit of Electric Flux. Measuring unit of Electric Flux is symbolized by “Φe”.
1Vm=1Volt•1meter
The relationship between quantities can be written using words or symbols (letters), but symbols are normally used because they are much shorter.
मात्राओं के बीच के संबंध को शब्दों या प्रतीकों (अक्षरों) का उपयोग करके लिखा जा सकता है, लेकिन प्रतीकों का उपयोग आमतौर पर इसलिए किया जाता है क्योंकि वे बहुत छोटे होते हैं।
For example,
V is used for voltage, I for current, and R for resistance:
As a word equation: voltage = current × resistance
The same equation using symbols: V = I × R
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