Many kinds of units of measurements have been used indigenously in different places over different periods of time and new units have been introduced as and when needed. But the need for universal conformity gave birth to the standard system of measurements, what is known as the S.I. unit today.
What is the S.I. Unit of Measurement?
The S.I. unit is actually an abbreviation of the French word “Système International”. The S.I. unit is the standard system of measurements which are universally accepted and used for technical publishing and scientific research.
International System of Units
Earlier, people didn't have measuring units to calculate the standard measurement units. So, they came up with unique ways of measurement with the tools which were available to them. The foot was used as a measurement for length. 1 foot was calculated as .
To solve the problem of different measurements, a common system of units called the international system of units was found and accepted. This is the modern version of the metric system. Though this system is now being used in all fields including science and technology, some people, especially in the USA, refer to length as foot and inches instead of centimetres.
Apart from the seven base units of measurement, some units are calculated based on one or more base units. These units are known as derived units.
Examples of such units are
Power: watt (W)
Frequency: hertz (Hz)
There are seven base units measurements namely meter, kilogram, second, ampere, kelvin, mole, and candela.
(Image will be uploaded soon)
The most common among these are kilograms, seconds, and meters.
Why are Standard Units Used in Measurement?
Standard units are used in measurement for more accuracy. The measurement should be the same for all. As there needs to be uniformity in the measurement, we must have a common set of units in measurement. These are called standard units.
The standard unit is different for different quantities.
What is a Standard Unit of Measurement?
The standard unit of measurement is a value that is fixed and cannot be changed. It is needed to have uniformity in measurement. The measurement is measured as feet, inches, and pounds in the United States and meters, centimetres, and kilograms in the metric system.
Standard vs Non-Standard Measurements
There are two types of measurements, namely Standard and non-Standard.
Standard measurement units are those which are used within the measurement system such as ounces, inches, and pounds.
The Advantages of Standard Unit are:
It helps everyone to understand measurements in a set of unit systems.
SI units are derived from one another without the use of conversion
SI is a metric system. The disadvantages are that the SI unit talks only about one unit. Hence other units' importance was diluted.
Nonstandard measurement units are those which are not used like a pencil, arm, and block.
The advantage of Nonstandard measurement is it makes measurement easier while the disadvantage is it might be tough for many to understand.
Advantage of SI Units
SI units are measured all over the world.
There is only one unit for each quantity.
Submultiples and multiples can be expressed as multiples of ten as it is a metric system
Measurement of Physical Quantities
A physical quantity is the property of an object that can be measured. Examples of physical quantities are the mass of a body or the length of an object. There are two types of physical quantities namely base quantities and derived quantities.
Base quantities are length, mass, time, luminous intensity, temperature, current, and amount of substance
Derived quantities are those which are derived from other physical quantities. Ex acceleration, velocity, and force.
SI Unit Prefixes
The SI system uses a standard system of prefixes to the basic units which makes it more relevant.
Prefixes are used to identify the fractions Ir multiples of the basic unit. There are 20 acceptable prefixes.
SI Base Units
These units of measurement are considered to be the fundamental units and all the other units can be derived from the SI base units.
Unit of Mass (kilogram): Kilogram is defined by taking the fixed value of Planck’s constant in kilogram per meter square per second. It is abbreviated as kg.
Unit of Length (Meter): Abbreviated as “m”, meter is defined by taking the value of speed of light in vacuum in meter per second.
Unit of Time (Second): A second is defined as the value obtained by taking the value of each Cesium frequency. Its abbreviation is “s”.
Unit of Electric Current (Ampere): Abbreviated as “A”, it is obtained by taking the fixed value of elementary charge.
Unit of Temperature (Kelvin): Although Fahrenheit and Celsius are the more commonly used measurements of temperature, the SI unit of temperature is Kelvin, abbreviated as K. Its value is equal to the Boltzmann constant. 10C = 273 K.
Unit of an Amount of Substance (Mole) : One mole contains 6.02214076×1023 elementary entities which is the constant of Avogadro’s number and is expressed as mol-1.
Unit of Luminous Intensity (Candela) : Defined by the fixed value of luminous efficacy, the SI unit of luminous intensity is candela and is expressed as “cd”.
Note: The 7 base units are considered to be mutually independent from which the other units of measurement can be derived.
The derived SI units are unlimited and are in a continuous process of development resulting from scientific research and can be based either solely on the base units or they can be a combination of base units and other already established derived units.
There are a few additional SI units that are very commonly used in Physics, such as, “joule” which is the SI unit of heat and “Tesla” which is the SI unit of magnetic field.
Students are suggested to have a thorough understanding of these units in Physics and their dimensions. Vedantu's notes, important questions and revision topics will help you clear your basics on SI unit of measurement. You can even download the references for free! Go ahead with a curious mind and come back as a champ!