The unit of measurement is a standardized quantity of physical properties and is used as a factor to represent the amount of occurrence of the property. The units of measurement radiation is one of the earliest tools invented by mankind. Primitive society required basic measures to accomplish many tasks: building homes of the right size and shape, making clothing, or bartering food or raw materials.

The unit of measurement is a clear magnitude of the quantity defined and adopted by the convention or law, which is used as a standard for measuring the same kind of quantity.

Measurement is a process of determining the size of a physical quantity compared to a basic reference quantity of the same kind. Now there is a global standard, the International System of Units (SI), a modern form of the metric system. In trade, weights and measures are usually the subject of government regulation to ensure fairness and transparency.

The task of the International Bureau of Weights and Measures (Bipm) is to ensure the global uniformity of measurements and their traceability to the International System of Units (SI).

**CONTENT**

**I) RADIATION QUANTITIES**

THE CONCEPT OF RADIATION

UNITS OF MEASUREMENT RADIATION

**II) FUNDAMENTAL QUANTITIES**

THE CONCEPT OF FUNDAMENTAL QUANTITIES

FUNDAMENTAL UNITS

**III) DERIVED QUANTITIES**

THE CONCEPT OF DERIVED QUANTITIES

DIMENSIONS AND UNITS OF DERIVED QUANTITIES

**I) RADIATION QUANTITIES**

**THE CONCEPT OF RADIATION**

Radiation is the rate of heat transfer through the emission or absorption of electromagnetic waves.

The rate of heat transfer depends on the surface area and the fourth power of the absolute temperature: Qt=σeAT4Qt=σeAT4,

where σ = 5.67 × 10^{−8}J/s ⋅ m^{2} ⋅

K^{4} is the Stefan-Boltzmann constant and e is the emissivity of the body.

For a black body, *e *= 1 whereas a shiny white or perfect reflector has *e* = 0, with real objects having values of e between 1 and 0.

The net rate of heat transfer by radiation is Qnett=σeA(T42−T41)Qnett=σeA(T24−T14) where *T*_{1} is the temperature of an object surrounded by an environment with uniform temperature *T*_{2} and *e* is the emissivity of the object.

### UNITS OF MEASUREMENT RADIATION

Here are units to measure radiation dose and exposure:

**rad or radiation absorbed dose**

The amount of radiant energy absorbed in a certain amount of tissue.**gray (Gy)**

A unit of absorbed radiation equal to the dose of one joule of energy absorbed per kilogram of matter, or 100 rad. The unit is named for the British physician L. Harold Gray (1905-1965), an authority on the use of radiation in the treatment of cancer.**milligray (mGy)**

A unit of absorbed radiation equal to one thousandth of a gray, or 0.1 rad.**rem or roentgen-equivalent-man**

A unit of measurement that takes into account different biological responses to different kinds of radiation. The radiation quantity measured by the rem is called equivalent dose.**millirem**

One thousandth of a rem, the unit for measuring equivalent dose.**roentgen (R, r)**

The international unit of exposure dose for x-rays or gamma rays. Roentgens are named after Professor Wilhelm Konrad Roentgen, the man who discovered x-rays in 1895.**sievert (Sv)**

The unit for measuring ionizing radiation effective dose, which accounts for relative sensitivities of different tissues and organs exposed to radiation. The radiation quantity measured by the sievert is called effective dose.**millisievert (mSv)**

One thousandth of a sievert, the unit for measuring effective dose.

### II) FUNDAMENTAL QUANTITIES

**THE CONCEPT OF FUNDAMENTAL QUANTITIES**

The Fundamental Quantity is independent Physical Quantity that is not possible to express in other Physical Quantities. It is used as pillars for other quantities such as Derived Quantities. In Physics, Length, Mass, Time, Electric Current, Thermodynamic Temperature and others are examples of Fundamental Quantities.

Area

Density ”

**The seven fundamental S.I units are:−**

metre → for length

second → for time

kilogram → for mass

kelvin → for temperature

ampere → for electric current

candela → for luminous intensity

mole → for the amount of substance.

**FUNDAMENTAL UNITS**

A fundamental unit is a unit adopted for measurement of a base quantity. A base quantity is one of a conventionally chosen subset of physical quantities, where no subset quantity can be expressed in terms of the others.

* Length (meter)

* Mass (kilogram)

* Time (second)

* Electric current (ampere)

* Thermodynamic temperature (kelvin)

* Amount of substance (mole)

* Luminous intensity (candela)

- II) DERIVED QUANTITIES

THE CONCEPT OF DERIVED QUANTITIES

Derived quantities are quantities that are calculated from two or more measurements. Derived quantities cannot be measured directly. They can only be computed. Many derived quantities are calculated in physical science. Three examples are area, volume, and density.

DIMENSIONS AND UNITS OF DERIVED QUANTITIES

QUANTITY | UNIT | UNIT ABBREVIATION | DERIVATION |

Area | Square meter | m^{2} |
Length x width |

Volume | Cubic meter | m^{3} |
Length x width x height |

Density | Kilograms/cubic meter | Kg/m^{3} |
Mass/volume |

Concentration | Mole/Litre | Mol/L | Amount/Volume |

Speed | Meters/second | m/s | Length/time |

Acceleration | Meter/second square | m/s^{2} |
Speed/Time |

Force | Newton | N | Mass x Acceleration |

Energy | Joule | J | Force x Length |

Units and measurements :- Physical quantity dimensions, units, measurement of length, volume, mass, weight and time.

Derived Formulas examples:

Speed = __distance__ = __L__=> LT ^{-1} (ms^{-1})

time T

Velocity = __displacement__ = __L__ => LT^{-1} (ms^{-1})

Time T

Acceleration = __velocity__ = __LT ^{-1}__ => LT

^{-2}(Ms

^{2})

time T

Force = Mass x acceleration = Mx LT^{-2} => MLT ^{-2}

Example:- Show that V = U + at is dimensionally correct

Note that V = final velocity

U = lower velocity

Therefore there formulas are the same

V = U = LT^{-1}

From V = U + al

LT^{-1} = LT^{-1} + LT^{-2} x T^{-1}

LT^{-1} = LT^{-1} + LT^{-2}

Since all sides are the same then it is dimensionally correct.