In today's article, we are going to give information about various physical quantities and their SI units. Questions related to this topic are often asked in competitive exams, so read this article carefully. 

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Physical quantities and their SI units 

First of all, let us know what is physical quantity.

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What is a Physical quantity? 

A physical quantity is a property of a material or system that can be determined by measurement.

Types of physical quantities 

Physical quantities can be divided into two parts - 

Scalar quantity and vector quantity

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Scalar quantity 

Those quantities which have only magnitude and no direction are called scalar quantities. Scalar quantities are expressed by a magnitude and a numerical value. 

For example - if the height of a building is 40 meters then the height of the building is a scalar quantity because it only gives a numerical value of 40 and the magnitude of the height in meters to express the height. No direction is given in it. 

Examples - mass, speed, volume, work, time, distance, temperature, energy, density, electric current, pressure, etc. 

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Vector quantity

Those quantities which have magnitude as well as direction are called vector quantities. Vector quantities are expressed by magnitude, numerical value, and direction. 

For example - If a person is going to his home by driving a car at a speed of 35 km/hr in the south direction, then velocity is a vector quantity because it has a numerical value of 35, magnitude 35 km/hr, and direction south to express the velocity. 

Examples -  displacement, velocity, force, acceleration, momentum, weight, impulse, torque, current, angular velocity, magnetic intensity, magnetic intensity etc. 

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What is a unit?

The unit is a standard reference used to measure a physical quantity. 

Types of units 

There are two types of units - Fundamental units and Derived units. 

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Fundamental unit 

The units used to express a physical quantity that is independent of other units are called fundamental units. Their number is 7.

Meter, Second, Kilogram, Ampere, Mole, Kelvin, Candela.

Derived unit 

When two or more fundamental units are required to express a physical quantity, then it is called derived unit. 

Such as force, work, acceleration, energy, etc. 

What are the unit systems?

The following four methods are used for the measurement of physical quantities -

1. CGS method,
2. FPS method,
3. MKS method,
4. SI method. 

CGS Methodology 

In this system, the unit of length is centimeter, the unit of mass is gram and the unit of time is second. Therefore, it is called the Centimetre Gram Second or CGS system. It is also called the French or Metric system. 

FPS Method 

In this system, the unit of length is foot, the unit of mass is pound and the unit of time is second. Hence it is called Foot Pound Second or FPS system. It is also called the British system. 

MKS methodology 

In this system, the unit of length is meter, the unit of mass is kilogram and the unit of time is second. Therefore, it is called a Metre Kilogram Second or MKS system.

International System of Units/SI System

In 1960, SI was accepted by the International Weights and Measures Conference, whose full name is (International System of Units or SI Units). This is an enhanced form of the MKS system. 

In this system, there are seven basic units and two supplementary units. 

The 7 fundamental units and 2 supplementary units of the SI system are given in the table below. 

Major Physical Quantities and SI Units 

Some important physical quantities and their SI units are given in the table below -

Note: The unit of force in the CGS system is dyne and the unit in the SI system is newton. 

1 newton = 10 ⁵ dynes 

The unit of work in the CGS system is erg and in the SI system, the unit is joule. 

1 joule = 10 ⁷ ergs 

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Some other Important Units 

The units used to measure very long distances are as follows -

Astronomical unit : 

The distance between the Sun and the Earth is called the 'Astronomical Unit' (AU). 

1 astronomical unit = 1.495 x 10¹¹meters

Light year :

A light year is the distance traveled by light in a vacuum in one year. Light year is used to measure astronomical distances because the speed of light always remains the same. 

1 light year = 9.46 x 10 ¹⁵ meters

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Parsec :

 This is the largest unit of measuring distance.

1 parsec = 3.26 light years 

1 parsec = 3.08 x 10¹⁶ meters

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Conclusion 

In today's article, we have given you information about various physical quantities and their SI units . Hope you liked the information given by us. You can also share this article with your friends. 

Also, if any question related to this article comes to your mind, then you can ask us in the comment box given below. 

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