Units and Measurement Practice Flashcards

Vocabulary practice flashcards based on lecture notes covering the categorization of units, SI standards, precision through significant figures, and the application of dimensional analysis.

Unit

A basic, arbitrarily chosen, internationally accepted reference standard used as a comparison for the measurement of any physical quantity.

Fundamental Units

The units for the base quantities (such as length, mass, and time) which serve as the foundation of a system of units.

Derived Units

Units obtained for physical quantities that are expressed as combinations of the fundamental or base units.

System of Units

A complete set of measurement units that includes both the base units and the derived units.

SI (Système International d’ Unités)

The international system of units, recently revised in 2018, which uses seven base units and a decimal-based scheme of symbols and abbreviations.

Radian ($\text{rad}$)

The unit defined for plane angle $d\theta$ as the ratio of length of arc $ds$ to the radius $r$, expressed as $d\theta = \frac{ds}{r}$, which is a dimensionless quantity.

Steradian ($\text{sr}$)

The unit defined for solid angle $d\Omega$ as the ratio of the intercepted area $dA$ of the spherical surface to the square of its radius $r^2$, expressed as $d\Omega = \frac{dA}{r^2}$, which is a dimensionless quantity.

Significant Figures

The reliable digits in a measured value plus the first digit that is uncertain, serving to indicate the precision of a measurement.

Scientific Notation

The reporting of measurements in the form $a \times 10^b$, where $a$ is a number between 1 and 10 and $b$ is a positive or negative exponent.

Order of Magnitude

The exponent $b$ of 10 when a quantity is rounded and expressed in the power of 10 as $10^b$, used to give an approximate estimate.

Dimensions

The powers or exponents to which base quantities (like [L], [M], [T]) are raised to represent a physical quantity.

Dimensional Formula

An expression that shows which base quantities, and in what power, represent the dimensions of a specific physical quantity, such as volume being $[M^0 L^3 T^0]$.

Dimensional Equation

An equation obtained by equating a physical quantity with its corresponding dimensional formula.

Principle of Homogeneity of Dimensions

The principle stating that physical quantities may be added together or subtracted only if they have the same dimensions.

Mole ($\text{mol}$)

The SI unit for amount of substance, containing exactly $6.02214076 \times 10^{23}$ elementary entities, a number known as the Avogadro number.