Definitions Glossary

Term	Definition
Physical quantity	A measurable property of a physical phenomenon (e.g., mass, force, temperature)
Base quantity	A fundamental physical quantity defined independently of others (7 in SI)
Derived quantity	A physical quantity expressed as a combination of base quantities (e.g., velocity = length/time)
SI unit	The internationally agreed unit of measurement for each physical quantity
Dimensional formula	An expression showing how a physical quantity is related to base dimensions M, L, T (e.g., [ $M^{1}$$L^{1}$$T^{-2}$ ])
Dimensional analysis	A method using dimensions to check equation correctness, derive formulas, or convert units
Dimensionless quantity	A physical quantity with no units or dimensions (e.g., refractive index, strain, angle in radians)
Significant figures	The digits in a measurement that carry meaningful information about its precision
Absolute error	The magnitude of the difference between measured and true values; has the same units as the quantity
Relative error	The ratio of absolute error to the true (or mean) value; dimensionless
Percentage error	Relative error expressed as a percentage: ( $\Delta A$ /A) × 100%
Systematic error	A consistent, reproducible error due to instrument faults, calibration issues, or personal bias
Random error	An unpredictable fluctuation in measurement due to uncontrollable variables
Zero error	A type of systematic error where an instrument reads a non-zero value when the measured quantity is zero
Least count	The smallest value measurable by an instrument; determines the precision of measurement
Precision	How close repeated measurements are to each other (reproducibility); relates to random error
Accuracy	How close a measurement is to the true value; relates to systematic error
Error propagation	The method of calculating total error in a derived quantity from errors in its component measurements