SI Base & Derived Units
The International System of Units (SI), maintained by the General Conference on Weights and Measures (CGPM), standardizes scientific measurement across seven base physical quantities: meter (length), kilogram (mass), second (time), ampere (electric current), kelvin (thermodynamic temperature), mole (amount of substance), and candela (luminous intensity). The historic 2019 redefinition grounded these units entirely in fundamental invariants, including the Planck constant ($h$), speed of light ($c$), and elementary charge ($e$). Derived units quantify complex physical interactions, expressing force in Newtons ($kg\cdot m/s^2$), pressure in Pascals ($N/m^2$), electrical potential in Volts ($W/A$), and capacitance in Farads ($C/V$). Competitive examinations regularly assess base dimensions, prefix multiples from pico- to tera-, and dimensional consistency in physical equations.
Key Concepts & Examination Highlights
- The seven SI base units are meter (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd).
- The 2019 CGPM redefinition fixed the numerical value of Planck's constant at exactly $6.62607015 \times 10^{-34} J\cdot s$ to define the kilogram.
- Pressure is measured in Pascals ($Pa$), where $1 Pa = 1 N/m^2 = 1 kg\cdot m^{-1}\cdot s^{-2}$.
- Electrical capacitance is expressed in Farads (F), defined as one Coulomb of charge per Volt of potential difference.