Si Units List - Definition, Advantages, FAQs

Edited By Team Careers360 | Updated on Nov 12, 2024 11:25 PM IST

What is unit?

The term unit indicates the amount or magnitude of any quantity which is measurable. Different units are used to indicate different measurements of particular kind of quantities.

What is unit in Physics?

In physics, there are a lot of physical quantities which are measured to perform an experiment and a lot of physical quantities which form the basis of mathematical equations which govern laws of physics such as length, mass and many more. In order to measure such physical quantities, Appropriate units are made to measure them accurately.

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What is unit?
What is SI unit?
Advantages of SI units:

Si Units List - Definition, Advantages, FAQs

What is SI unit?

The term SI stands for International system of units. This is the standard system of measurements of units which is used by all the countries to measure any physical quantities. It was made to resolve the issue of different units used by different countries to measure a particular physical quantity.

The SI unit system consists of seven fundamental physical quantities units and these are fundamental because any other physical quantity in physics can be derived from these quantities relations. Any Physical quantity unit which is derived from fundamental physical quantities is known as Derived units.

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Fundamental Physical Quantities:

In physics, there are seven fundamental physical quantities which form the basis for deriving any other physical quantities. These seven fundamental physical quantities are listed as:

Length
Time
Mass
Electric current
Luminous intensity
Amount of substance
Temperature.

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Definition, Symbols and SI units List of Fundamental physical Quantities:

Below is the SI unit list chart indicating their definition, symbols along with their SI unit.

Quantity Name	Definition	SI Unit	Symbol
Length	Length is defined as the distance between two points of any object.	meter	m
Time	Time is the sequence of events that occurred in nature.	second	s
Mass	Mass is defined as the total amount of matter present in a body.	Kilogram	s
Electric current	Electric current is defined as the flow of electric charges inside a material.	Ampere	A
Luminous Intensity	Luminous Intensity is the total amount of visible light emitted in a unit of time per unit of solid angle.	Candela	Cd
Amount of Substance	The measurement of the number of atoms or molecules inside a material is called Amount of substance.	Mole	mol
Temperature	The measurement of intensity of heat inside a body is called temperature.	Kelvin	K

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Define Derived Units.

In physics, other than these seven fundamental physical quantities, any physical quantity can be derived from the relationship between these fundamental physical quantities and hence, these quantities are called derived quantities and units of such quantities are known as derived units.

Some of the most common and used derived units are listed below with their definition, SI units and their symbols.

Quantity Name	Definition	SI unit	symbol
Area	It’s the amount of space covered by an object in two dimensional plane	meter square	m²
Volume	It’s the amount of space covered by an object in three dimensional space.	meter cube	m³
Velocity	Velocity is the ratio of distance covered by a body over time.	meter per second	ms^-1
Acceleration	Acceleration is the ratio of velocity of a body over time.	meter per second square	ms^-2
Force	The product between mass of a body and the acceleration produced in it is called Force.	Newton	N
Frequency	The number of oscillations of a body in one second is called frequency.	Hertz	Hz
Work	The product of force applied on a body and the displacement covered by it is known as work done.	Joule	J
Pressure	Pressure is the ratio between force acting on a body to the area to which force is applied.	Pascal	Pa
Power	Power is defined as the ratio of work done by a body over a given period of time.	Watts	W
Density	Density is defined as the ratio between mass and volume of a body.	Kilogram per meter cube	Kgm^-3

These are some derived units and there are more, in brief other than those seven fundamental physical quantities every quantity which is measurable in physics will be derived from those seven fundamental physical quantities and their SI unit name and symbol is after the scientist who discovered a particular kind of physical quantity. For example, It was. Isaac Newton who gave the idea of force so, SI unit of force or derived unit of force is called Newton, named after S. Isaac Newton.

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Different units for measurement of most used fundamental physical quantities other than SI base units:

In physics, a single physical quantity can be measured in many different units with respect to their SI units due to their very large numerical values sometimes, some of most used Fundamental physical quantities can also be measured in different units are listed as”

Length:

Since, The SI unit of length is meter and its symbol is m. Along with this unit, following are most common used units for the measurement of length are given in unit table as:

Name of unit	Symbol	Relation with SI unit of Length (m)
Centimetre	cm	1m=100cm
Nanometre	nm	1nm=10^-9m
millimetre	mm	1mm=10^-3m
decimetre	dm	1dm=0.1m
Angstrom	A°	1A°=10^-10m
Kilometre	Km	1km=1000m
Yard	yd	1yd=0.914m
Inch	in	1in=0.0254
foot	ft	1ft=0.305m

Time:

Since, The SI unit of time is second and its symbol is s. Along with this unit, the following are most commonly used units for the measurement of time are given in the unit table:

Name of Unit	Symbol	Relation with SI unit of Time (s)
Minute	min	1min=60s
Hour	hr	1hr=3600s
Day	Day	1day=24hr
Year	yr	1yr=365days

Mass:

Since, The SI unit of mass is Kilogram and its symbol is Kg. Along with this unit, the following are most commonly used units for the measurement of mass are given in the unit table:

Name of unit	Symbol	Relation with SI unit of Mass (Kg)
Grams	gm	1Kg=1000gm
Decigram	dgm	1dgm=0.1gm
Centigram	cgm	1cgm=0.01gm

Advantages of SI units:

From country to country, we don’t need to convert one unit of any physical quantity measured to another system of units, SI unit provide standard unit used by all countries in the scientific field. This is the most important advantage of using SI unit.
Some physical quantities have very long expressions for their measurements of units, SI unit provide special memorable symbols for each fundamental physical quantity SI units which are easy to represent the unit of measurement of any physical quantity.
The fundamental physical quantities are used to determine units of measurements of other physical quantities known as derived units so, the SI unit of fundamental physical quantities gives the advantage to derive any physical quantity SI unit.

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NCERT Physics Notes:

Frequently Asked Questions (FAQs)

1. What is fundamental Physical Quantity?

In physics, there are seven fundamental physical quantities which are the basis in SI units system to derive any desired physical quantity. These seven fundamental physical quantities are listed below along with their SI units and symbols.

Length. SI unit of length is called a metre having symbol as m.
Time. SI unit of time is called the second having a symbol as s.
Mass. SI unit of mass is kilogram having symbol as kg.
Electric current. SI unit of electric current is called an ampere symbol as A.
Luminous Intensity. SI unit of luminous intensity is called candela having the symbol as Cd.
Amount of substance. SI unit of amount of substance is called mole having symbol as mol.
Temperature. SI unit of temperature is called kelvin having the symbol as K.

2. What is SI unit of time?

The SI unit of time is known as seconds and the symbol is denoted as s. It is one of the fundamental physical quantities which is listed in SI units of measurement.

3. What is derived units?

There are seven fundamental physical quantities namely Length, Mass, Time, Luminous Intensity, Electric current, Amount of substance, Temperature. Other than these seven fundamental physical quantities listed by International system of units, all the physical quantities SI units can be derived from these seven units such as Area, Volume, Frequency and many more useful physical quantities, these are all derived from seven fundamental physical quantities hence known as derived units.

4. Which of the following is a derived unit? (A) Second (B) Kilogram (C) Newton (D) Ampere

According to International system of units, seven fundamental units are Length(metre), Time (seconds), Temperature (Kelvin), Luminous Intensity (Candela), Amount of substance (mole), Mass (Kilogram), Electric current (Ampere). Any SI unit other than these seven is called Derived quantities, so from given options Newton which is a derived SI unit of physical quantity Force is a derived unit. Hence, the correct option is (C) Newton, is a derived unit.

5. What is the unit meaning?

The term SI stands for International system of units, which is made to establish the common reference of measurements of all the physical quantities. The units defined by International system of units (SI units) are accepted by all the countries and use these standard units for measurement of all the physical quantities in scientific fields.