PHYSICS

Unit and Measurement: In Physics, measurement is the process of comparing a physical quantity with a standard unit. A unit is a fixed standard used to express the magnitude of a physical quantity, such as metre (m) for length and kilogram (kg) for mass.

Important Derived Units, Word Formulas & Dimensions

Physical Quantity	Word Formula	Dimensional Formula	SI Unit (Special Name)	CGS Unit	Key Exam Notes
Force	Mass Acceleration	[MLT^-2]	Newton	Dyne	1 Newton = 10⁵ dynes
Work / Energy	Force Displacement	[ML² T^-2]	Joule	Erg	1 Joule = 10⁷ ergs
Power	Work Done Time Taken	[ML² T^-3]	Watt	Erg per second	1 Horsepower = 746 Watts
Pressure / Stress	Force Area	[M L^-1 T^-2]	Pascal	Barye	1 bar = 10⁵ Pascals
Linear Momentum	Mass Velocity	[M L T^-1]	Newton-second	Gram Centimetre per second	Same dimension as Impulse (Force × Time Interval)
Frequency	One ÷ Time Period	[M⁰ L⁰ T^-1]	Hertz	Cycles per second	Reciprocal of time
Electric Charge	Electric Current × Time	[AT]	Coulomb	Statcoulomb	1 Coulomb 3 × 10⁹ Statcoulombs
Potential Difference (Voltage)	Work Done ÷ Electric Charge	[M L² T^-3 A^-1]	Volt	Statvolt	1 Statvolt = 300 Volts
Electric Resistance	Potential Difference ÷ Electric Current	[M L² T^-3 A^-2]	Ohm	Statohm	Derived from Ohm’s Law
Electric Capacitance	Electric Charge ÷ Potential Difference	[M^-1 L^-2 T⁴ A²]	Farad	Statfarad	Microfarad and Picofarad are practical units
Magnetic Flux	Magnetic Field × Area	[M L² T^-2 A^-1]	Weber	Maxwell	1 Weber = 10⁸ Maxwells
Magnetic Field Strength	Force ÷ (Electric Current × Length)	[M L⁰ T^-2 A^-1]	Tesla	Gauss	1 Tesla = 10⁴ Gauss
Inductance	(Induced Voltage × Time) ÷ Change in Current	[M L² T^-2 A^-2]	Henry	Abhenry	1 Henry = 1 Weber per Ampere
Surface Tension	Force ÷ Length	[M L⁰ T^-2]	Newton per metre	Dyne per centimetre	1 Newton per metre = 10³ dynes per centimetre
Viscosity (Dynamic)	(Force × Distance) ÷ (Area × Velocity)	[M L^-1T^-1]	Pascal-second	Poise	1 Pascal-second = 10 Poise

Key Constants

Physical Constant	Word Formula	Dimensional Formula	SI Unit
Universal Gravitational Constant	(Gravitational Force × Distance squared) ÷ (First Mass × Second Mass)	[M^-1 L³ T^-2]	Newton metre²/kilogram²
Planck’s Constant	Energy of a Photon ÷ Frequency of Radiation	[M L² T^-1]	Joule second (Same as Angular Momentum)
Universal Gas Constant	(Pressure × Volume) ÷ (Amount of Substance in Moles × Absolute Temperature)	[M L² T^-2 K^-1 mol^-1]	Joule per mole per Kelvin