Units and Measurement Flashcards

Flashcards covering units and measurement concepts from a physics lecture.

Unit

Comparison with a basic, arbitrarily chosen, internationally accepted reference standard.

Measurement of a physical quantity

A number accompanied by a unit.

Fundamental or base units

Units for fundamental or base quantities.

Derived units

Units obtained for the derived quantities.

System of units

Complete set of units, both base and derived.

CGS system base units

Centimetre, gram, and second.

FPS system base units

Foot, pound, and second.

MKS system base units

Metre, kilogram and second.

Système Internationale d’ Unites (SI)

Internationally accepted system of units.

SI unit for plane angle

radian (rad)

SI unit for solid angle

steradian (sr)

Significant digits/figures

Includes all digits known reliably plus the first uncertain digit.

Best way to remove ambiguities in significant figures

Report every measurement in scientific notation (a × 10b).

Order of magnitude

The power b of 10 in scientific notation.

Multiplication/division rule (significant figures)

Final result retains as many significant figures as the original number with the least significant figures.

Addition/subtraction rule (significant figures)

Final result retains as many decimal places as the number with the least decimal places.

Rounding off Rule 1

Preceding digit raised by 1 if the insignificant digit to be dropped is more than 5.

Rounding off Rule 2 (when insignificant digit is 5)

If the preceding digit is even, the insignificant digit is dropped; if odd, the preceding digit is raised by 1.

Dimensions of physical quantities

Describes the nature of a physical quantity.

Dimensional formula

Expression showing how base quantities represent the dimensions of a physical quantity.

Dimensional equation

Equation equating a physical quantity with its dimensional formula.

Principle of homogeneity of dimensions

Used to check the correctness of an equation.