SI Units
Physics · SI इकाइयां · 25 facts
SI system adopted in 1960 at 11th General Conference on Weights and Measures (CGPM)
SI has 7 base units: metre, kilogram, second, ampere, kelvin, mole, candela
Length = Metre (m); Mass = Kilogram (kg); Time = Second (s)
Electric Current = Ampere (A); Temperature = Kelvin (K)
Amount of Substance = Mole (mol); Luminous Intensity = Candela (cd)
Force = Newton (N); Energy = Joule (J); Power = Watt (W)
Pressure = Pascal (Pa); Frequency = Hertz (Hz); Charge = Coulomb (C)
Resistance = Ohm (Ω); Voltage = Volt (V); Capacitance = Farad (F)
Magnetic Flux = Weber (Wb); Magnetic Field = Tesla (T); Inductance = Henry (H)
EXAM TRAP: Light Year, Parsec, AU are units of DISTANCE — NOT time
1 Light Year = distance light travels in 1 year = 9.46 × 10¹² km
1 Astronomical Unit (AU) = Earth to Sun distance = ~15 crore km
1 Newton = 10⁵ Dyne; 1 Joule = 10⁷ Erg (CGS conversions)
1 Horse Power (HP) = 746 Watts; 1 kWh = 3.6 × 10⁶ Joules
1 Bar = 10⁵ Pascal; 1 atm = 1.013 × 10⁵ Pascal = 760 mmHg
Angstrom = 10⁻¹⁰ m (atomic distances); Micron = 10⁻⁶ m; Nanometre = 10⁻⁹ m
Nautical Mile = 1.852 km (used in sea/air navigation)
Fathom = 6 feet = 1.83 m (depth in water); Furlong = 201.17 m
Speed of light in vacuum = 3 × 10⁸ m/s (fastest speed in universe)
Kilogram redefined in 2019 based on Planck constant (not physical prototype anymore)
Decibel (dB): sound intensity unit; Curie/Becquerel: radioactivity units
Knot = 1 nautical mile/hour (speed in sea navigation); Mach = ratio to speed of sound
Barrel = 159 litres (petroleum); Quintal = 100 kg; Metric Ton = 1000 kg
Dioptre: unit of lens power (1/focal length in metres); positive for convex, negative for concave
Candela replaced 'candle power' as SI unit of luminous intensity