SI units, or the International System of Units, are the standard units of measurement. They provide a consistent framework for measuring physical quantities.
Understanding SI units is crucial for real-world applications in physics, engineering, and daily life. In this post, we'll explore the complete SI units table in physics, including fundamental and derived units. We'll also provide examples to understand how these units are used in practice.
What are SI Units?
If we go deep into the history, before the adoption of SI units, different countries used various measurement units, leading to confusion and inconsistencies. It was harder to share physical quantities across borders. To address this, the International System of Units (SI) was established in 1960, providing a standardized system for measuring physical quantities.
The Seven Base SI Units
There are seven base SI units. They are based on seven fundamental quantities. These fundamental quantities are the building blocks for all other measurements. The seven base SI units are:
| Quantity | Unit | Symbol |
|---|---|---|
| Length | Meter | m |
| Mass | Kilogram | kg |
| Time | Second | s |
| Electric Current | Ampere | A |
| Temperature | Kelvin | K |
| Amount of Substance | Mole | mol |
| Luminous Intensity | Candela | cd |
The Derived SI Units Table in Physics
The SI units table in physics includes both base and derived units. Derived units are formed by combining base units through multiplication or division. Here's a comprehensive table of SI units used in physics:
| Quantity | Unit Name | Symbol | Expressed As | Example |
|---|---|---|---|---|
| Area | square metre | m² | m × m | Surface of a garden |
| Volume | cubic metre | m³ | m × m × m | Space inside a water tank |
| Speed / Velocity | metre per second | m/s | m ÷ s | Runner's speed (e.g., 5 m/s) |
| Acceleration | metre per second² | m/s² | m ÷ s² | Bike braking power |
| Force | newton | N | kg·m/s² | Pushing a shopping cart |
| Pressure | pascal | Pa | N/m² | Pressure in a car tyre ≈ 250,000 Pa |
| Energy / Work / Heat | joule | J | N·m | Energy to lift a book |
| Power | watt | W | J/s | Phone charger output ≈ 5 W |
| Electric Charge | coulomb | C | A·s | Charge moved in 1 sec by 1 A current |
| Electric Potential (Voltage) | volt | V | W/A | USB port voltage ≈ 5 V |
| Electric Resistance | ohm | Ω | V/A | Resistance of a toaster ≈ 20 Ω |
| Electric Conductance | siemens | S | 1/Ω | Conductance of saline solution |
| Magnetic Flux | weber | Wb | V·s | Magnetic flux in an electric motor |
| Magnetic Field Strength | tesla | T | Wb/m² | Magnetic field of a bar magnet ≈ 0.01 T |
| Inductance | henry | H | Wb/A | Inductance in car ignition coil |
| Luminous Flux | lumen | lm | cd·sr | Output of a flashlight ≈ 300 lm |
| Illuminance | lux | lx | lm/m² | Street lighting ≈ 50 lx |
| Radioactivity | becquerel | Bq | decays/s | Activity of a smoke detector |
| Absorbed Radiation Dose | gray | Gy | J/kg | Medical X-ray dose |
| Equivalent Radiation Dose | sievert | Sv | J/kg | Limit for airline crew ≈ 0.02 Sv/year |