Units and dimensions formulas and measurements in SI or CGS system in science are recommended by the International Union of Pure and Applied Chemistry (IUPAC). In the standard unit system or SI system, we used the seven base units and dimensions formulas of physical quantities for analysis, measurement, and conversion. We use units and dimensions of mass, length, and time for measurement and conversion of force, density, energy, work, heat capacity, pressure, surface tension, etc. These physical quantities can be derived from base units or dimensions data.
The SI unit of luminous intensity or candela is not needed in physics or chemistry learning but it is included only for the sake of completeness.
International System of Units
International unit systems or simply SI systems of units and dimensions are used for the measurement and study of most types of physical quantities. For the measurement of wavelengths or wavenumber in the electromagnetic spectrum, we used commonly the CGS system.
Length, mass, time, electric power, thermodynamics temperature, amount of substance, and luminous intensity are seven base physical quantities according to the International Union of Pure and Applied Chemistry (IUPAC).
Fundamental Quantities and their Units and Symbols
SI unit of seven fundamental quantities
Fundamental quantities
SI unit
Symbol for SI unit
length
meter
m
mass
kilogram
kg
time
second
s
electric current
ampere
A
thermodynamic temperature
kelvin
K
amount of substance
mole
mol
luminous intensity
candela
cd
From these basic fundamental units and dimensions data, we derived the unit and dimension of activation energy, concentration, density, enthalpy, entropy, force, free energy function, the specific heat of gas, solid substances, etc.
Definition of Units of Measurement
How Long is a Meter?
A meter is the SI unit of length. A meter is the length of the path traveled by light in a vacuum during a time interval of 1/299792458 seconds.
Definition of Kilogram
The kilogram is the SI unit of mass. It is the weight of the platinum-iridium polished cylinder which is kept at the International Bureau of Weights and Measures in a suburb of Paris, France. Platinum-iridium alloy is chosen due to its durability and resistance to corrosion.
Definition of Second
The second is the duration of 9192631770 periods of the radiation corresponding to the transition between two hyperfine levels of the f-block element cesium-133 atom in the ground state.
What is Ampere?
Ampere is that constant current folwing if we maintained two straight parallel conductors of infinite length which are placed one meter apart in a vacuum with negligible cross-section. The force produced between these two conductors is equal to 2 × 10−7 newtons per meter.
What is Kelvin Temperature?
Kelvin is the SI unit of temperature. It is the fraction of 1/273.16 of the thermodynamic temperature of the triple point of the water.
What is Mole in Science?
Mole or simply mol is the SI unit of the amount of substances. It is the amount of substance in a system that contains as many elementary entities as there are atoms in 0.012 kilograms of carbon-12.
Candela Meaning
The candela is the unit of luminous intensity. Candela means the direction of a source that emits monochromatic radiation of frequency 540 × 1012 hertz. The radiant intensity in that direction has 1/683 watt per steradian.
Unit Conversion Table
The below measurement table or chart is used to define the multiple and submultiple prefixes for unit conversion with the roman symbol.
Derived Units Examples
Unit of Force
The SI unit of force is Newton and it can be derived from Newton’s second law of motion. From Newton’s second law of motion,
Force (F) = mass (M) × acceleration (F)
Again, acceleration = velocity/time
= length/time2, where velocity = length/time
From the above equation or formula, the CGS unit of force = g cm s−2 or simply dyne and the SI unit of force = Kg m s−2 or simply newton.
Dimension of Force
From the dimension of length, mass, and time, the derived dimension of force = [M L T −2].
Relation Between Newton and Dyne
From the definition of newton,
1 Newton = (1 kg × 1 m)/(1 s)2
Again, 1 kg = 103 g, and 1 m = 102 cm
Therefore, 1 Newton = (103 g × 102 m)/(1 s)2
=105 g cm s−2 = 105 dyne
What is the Unit of Work and Energy?
From the definition of work,
the unit of work = unit of force × unit of displacement
Therefore, the CGS unit of work = g cm2 s−2 or simply erg. The SI unit of work = kg m2 s−2 or simply joule.
Dimension of Work
From the definition, the dimension of work = dimension of force × dimension of length = [M L T−2] × [L] = [M L2 T−2].
Joule to erg Conversion
From the definition joule,
1 Joule = 1 kg × (1 m)2/(1 s)2
Therefore, 1 Joule = 103 g × (102 cm)2/(1 s)2 =107 g cm2 s−2 = 105 erg
Unit of Energy
The ability to do work is termed energy. Therefore, the SI unit of energy is the joule, and the CGS unit of energy is erg. The unit of the different forms of energy like kinetic energy, potential, mechanical, internal, electromagnetic, and surface energy is the same.
Unit of Heat Energy
Heat is another form of energy for the production of work. It is different from energy because all the other forms of energy are completely converted into work but heat is not wholly converted into work. The unit and dimension of heat and energy are identical. The SI unit of heat joule.
What is the Unit of Power?
The rate at which energy is transferred or converted is called power. Therefore, the SI unit of power = energy/time. From the above formula, the SI unit of power is joule/s or watt in honor of Scottish inventor James Watt.
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