Units and Measurements

Units and Measurements

The chosen standard used for measuring a physical quantity is called unit. Units are of two types - Fundamental Units and Derived Units.

Fundamental Units - The physical quantities which do not depend upon other quantities are known as Fundamental Quantities. Fundamental Units are the units of fundamental quantities.

Derived Units - Many units have also arisen from the basic/fundamental units. These are the 'derived units'. All the units which are defined or expressed in terms of fundamental units are called Derived Units. Several Systems of unit have been in use for describing measurement. The common systems are the C.G.S system based upon basic units such as centimetre, gram and second. F.P.S system (foot, pound, second) which is the British system. M.K.S system based upon basic units such as metre, kilogram and second.

S.I units – S.I units is the modified form of M.K.S system. System of International units, abbreviated as S.I units is the internationally accepted system. Today, the SI unit is accepted as the basic unit throughout the world. SI units began to be used worldwide in 1960. Various measurements in the scientific world are presented in SI units. In this system there are seven fundamental units and three supplimentary units. The seven fundamental units are metre, kilogram, second, ampere, kelvin, candela, mole. radian and sterdian are supplementary units.

Fundamental Units (Quantity, SI Unit & Symbol)

■ Length - metre (m)

■ Mass - kilogram (kg)

■ Time - Second (s)

■ Temperature - kelvin (K)

■ Electric Current - ampere (A)

■ Luminous Intensity – candela (cd)

■ Unit of Particle – mole (mol)

Supplementary Units (Quantity, SI Unit & Symbol)

■ Plane Angle – radian (rad)

■ Solid Angle – sterdian (sr)

Important Derived Units (Quantity, SI Unit & Symbol)

■ Force - newton (N)

■ Distance and Displacement - metre (m)

■ Velocity and Speed - metre/second (m/s)

■ Acceleration - metre/second² (m/s²)

■ Pressure - newton/metre, pascal (Pa)

■ Work and Energy - joule (J)

■ Power - watt (W)

■ Frequency - hertz (Hz)

■ Intensity of Sound - decibel (dB)

■ Intensity of Electric Field - newton/coulomb (N/C)

■ Intensity of Magnetic Field - tesla (T)

■ Potential Difference - volt (V)

■ Electric Charge – coulomb (C)

■ Electric Conductance - siemens (S)

■ Electric Current – ampere (A)

■ Electric Resistance - ohm (Ω)

■ Electric Capacitance - farad (F)

■ Resistivity - Ohm metre (Ωm)

■ Radio Activity - curie, rutherford, becquerel (Bq)

■ Distance of Stars - light year (ly)

■ Power of Lens - dioptre (dpt or D)

■ Illuminance - lux (lx)

■ Inductance - henry (H)

■ Magnetic Flux – weber (Wb)

■ Wave Length - metre (λ)

■ Area - square metre (m²)

■ Volume – cubic metre (m³)

■ Speed – metre per sec (ms^-1)

■ Momentum – kg metre/sec (kgm/s)

■ Power of Machines – horse power (hp)

Units of Length in Metre

■ 1 millimetre (mm) - 10^-3 metre

■ 1 centimetre (cm) - 10^-2 metre

■ 1 Micron (µm) - 10^-6 metre (Microns is the unit of distance defined in terms of micrometre. Used commonly in Biology)

■ 1 nanometre (nm) - 10^-9 metre (used by optical designers)

■ 1 Angstrom (A°) - 10^-10 metre

■ 1 Astronomical Unit (AU) – 1.496 x 10¹¹ metre (It is another unit of distance in space. It is the mean distance between earth and sun. One light year contains nearly 63282 Astronomical Units)

■ 1 Light Year - 9.46 x 10¹⁵ metre (Light Year is the distance travelled by light in vacuum in one year at a speed of 3 x 10⁸ m/s. Light Year is a unit of distance used in astronomy.)

■ 1 Par sec (parallactic second) - 3.08 x 10¹⁶ metre or 3.26 Light Year (The largest unit of Distance is par sec)

Conversion of Units

■ 1 Nautical Mile - 1.852 kilometre

■ 1 Mile - 1.60 kilometre

■ 1 Yard – 0.91 metre

■ 1 Feet – 0.3 metre

■ 1 Inch - 2.54 centimetre

■ 1 Horse Power – 746 watt

■ 1 Pound - 0.454 kilogram

■ 1 Square feet – 0.09 square metre

■ 1 Acre – 10⁴ square metre

■ 1 Hectre - 2.471 Acre

■ 1 Litre – 1000 cubic cm

■ 1 Ounce – 28.35 gram

■ 1 Gallon - 4.546 litre

■ 1 Barrel - 159 litre

■ 1 Feet – 12 inch

■ 1 Yard - 3 feet

■ 1 Mile – 5280 feet

■ 1 Nautical Mile – 6080 feet

■ 1 Fathom – 6 feet

■ 37° Centigrade – 98.6 ° Fahrenheit

■ 32° Fahrenheit - 0° Centigrade

■ 60 seconds - 1 minute

■ 60 minutes – 1 hour

■ 90° - Right Angle

■ 180° - Semi Circle

■ 360° - Circle

Temperatures

A thermometer is used to measure ambient temperature and is filled with mercury. The three units used in thermometers are Celsius, Fahrenheit, and Reaumur. According to the Celsius system, water freezes at zero degrees Celsius and boils at 100 degrees Celsius. According to the Fahrenheit system, water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit.

■ -273°C - The lowest temperature that can be reached is absolute zero.

■ -230°C - The temperature of Pluto's atmosphere.

■ -89.2°C - The lowest temperature ever recorded on Earth (in Antarctica).

■ -39°C - Mercury turns solid.

■ 0°C - Water freezes

■ 4°C - Maximum density of water

■ 36.8°C - Human body temperature

■ 37°C - Optimum temperature for egg hatching

■ 41°C - Body temperature of birds

■ 58°C - Highest temperature ever recorded on Earth (in Libya)

■ 100°C - Water boils

■ 250°C - Wood catches fire

■ 500°C - Optimum temperature used in ammonia production

■ 600°C - When cooking gas burns

■ 1063°C - Melting point of gold

■ 3410°C - Melting point of tungsten

■ 5500°C - Temperature of the surface of the Sun

■ 16 Million°C - Temperature at the center of the Sun

Units

■ Rainfall measurement unit - centimeter

■ Length measurement unit - meter

■ Area measurement unit - square meter

■ Radioactivity measurement unit - curie

■ Luminous intensity measurement unit - candela

■ Magnetic field strength measurement unit - tesla

■ Force measurement unit - newton

■ Resistance measurement unit - ohm

■ Pressure measurement unit - pascal

■ Power measurement unit - watt

■ Energy measurement unit - joule

■ Electric current measurement unit - ampere

■ Frequency measurement unit - hertz

■ Potential difference measurement unit - volt

■ Electric charge measurement unit - coulomb

■ Capacitance measurement unit - farad

■ Wavelength of light Unit of measurement - Angstrom

■ Unit of distance in space - Light year

■ Unit of power in machines - Horsepower

■ Unit of expansion - Cubic meter

■ Unit of distance to stars - Light year