Chapter 4: Common Derived Units

Derived units are formed by combining base units according to the algebraic relationship that defines the corresponding derived quantity. Many derived units, especially those used very frequently, are given their own special names and symbols in honour of pioneering scientists — for example, the unit of force is called the newton (after Sir Isaac Newton) rather than being written out every time as kg·m·s⁻². This chapter lists the most important derived units with special names, the physical quantity each measures, its defining formula, and its expression purely in terms of SI base units — a combination frequently tested in SSC and RRB general science papers.

4.1 Derived SI Units with Special Names

4.2 Other Frequently Used Derived Units (Without Special Names)

4.3 Named after Scientists — Quick Facts

SSC/RRB papers frequently test which scientist a given SI unit is named after. The newton honours Sir Isaac Newton (laws of motion and gravitation); the joule honours James Prescott Joule (mechanical equivalent of heat); the watt honours James Watt (steam engine pioneer); the pascal honours Blaise Pascal (fluid pressure); the volt honours Alessandro Volta (inventor of the voltaic pile, the first electric battery); the ohm honours Georg Simon Ohm (Ohm's law); the ampere honours André-Marie Ampère (electrodynamics); the coulomb honours Charles-Augustin de Coulomb (electrostatic force law); the farad honours Michael Faraday (electromagnetic induction and electrolysis); the henry honours Joseph Henry (self-inductance); the tesla honours Nikola Tesla (alternating current systems); the weber honours Wilhelm Eduard Weber (magnetism); the hertz honours Heinrich Rudolf Hertz (electromagnetic waves); the kelvin honours Lord Kelvin, William Thomson (thermodynamic temperature scale); and the becquerel, gray, and sievert honour Henri Becquerel, Louis Harold Gray, and Rolf Sievert respectively (radioactivity and radiation dose).