There are 2 types of physical quantities, the \(\color{Red}{\textbf{Fundamental}}\) and \(\color{Red}{\textbf{derived}}\) ones.

Fundamental quantities are those which do not depend upon other physical quantities, there are \(\color{Red}{\textbf{7 fundamental quantities}}\). They have own defined units.

\(\color{Red}{\textbf{Derived quantities}}\) are some function of the \(\color{Red}{\textbf{Fundamental quantities}}\), and they are infinite in number. Their units are depending on the units of \(\color{Red}{\textbf{Fundamental quantities}}\) in their dimensional analysis.

That's how quantities are defined, we all know this.

But do you know how \(\color{Green}{\textbf{UNITS}}\) are defined ?

(Note, here I don't mean that \(1 \text{ metre}\) is defined as \(100 cm\))

\(\color{Blue}{\textbf{Here are the 7 fundamental quantities}}\) \(\color{Blue}{\textbf{with their units and definition of their unit.}}\)

Their format- \( \color{Purple}{\textbf{Quantity}} \color{Green}{\textbf{---Unit}} \textbf{---Definition} \)

\(\mathbf{1.}\color{Purple}{\textbf{Mass}}-\color{Green}{\textbf{kilogram}}\)

The mass of a platinum-iridium cylinder kept in the National Bureau of Weights and Measurements, Paris

\(\mathbf{2.}\color{Purple}{\textbf{Length}}-\color{Green}{\textbf{metre}}\)

The distance travelled by light in vacuum in \( \dfrac{1}{299792458}^{th}\) part of a second or also defined as 1650763.73 times wavelength emitting from \(Kr^{86}\)

\(\mathbf{3.}\color{Purple}{\textbf{Time}}-\color{Green}{\textbf{second}}\)

The time interval in which Cesium-133 atom vibrates \(9192631770\) times.

\(\mathbf{4.}\color{Purple}{\textbf{Temperature}}-\color{Green}{\textbf{kelvin}}\)

\(\dfrac{1}{273.16}\) fraction of thermodynamic temperature of triple point of water.

\(\mathbf{5.}\color{Purple}{\textbf{Electric Current}} - \color{Green}{\textbf{ampere}}\)

The amount of electric current that produces a force of \(2\times 10^{-7} \textbf{N}\) per unit length, that acts between two parallel wires of infinite length and negligible cross-section area placed at 1m distance in vacuum.

\(\mathbf{6.}\color{Purple}{\textbf{Luminous Intensity}}-\color{Green}{\textbf{candela}}\)

The amount of intensity on \(\frac{1}{60000} m^2\) area of blackbody in the direction perpendicular to its surface at freezing point of platinum \(2042\) K at pressure of \(101325\) \(N/m^2\)

\(\mathbf{7.}\color{Purple}{\textbf{Quantity of substance}}-\color{Green}{\textbf{mole}}\)

The amount of substance which has same number of elementary entities as in 12 gm of carbon-12.

Source- NCERT textbook. (Felt like sharing because this was new to me and may be new to many of us!)

No vote yet

1 vote

×

Problem Loading...

Note Loading...

Set Loading...

Easy Math Editor

`*italics*`

or`_italics_`

italics`**bold**`

or`__bold__`

boldNote: you must add a full line of space before and after lists for them to show up correctlyparagraph 1

paragraph 2

`[example link](https://brilliant.org)`

`> This is a quote`

Remember to wrap math in \( ... \) or \[ ... \] to ensure proper formatting.`2 \times 3`

`2^{34}`

`a_{i-1}`

`\frac{2}{3}`

`\sqrt{2}`

`\sum_{i=1}^3`

`\sin \theta`

`\boxed{123}`

## Comments

Sort by:

TopNewestWell, the kilogram definition sucks. Since it was originally defined as, the cylinder has decreased mass compared to its sisters. But, there is a definition that could be better. Watch Sixty Symbols recent video on the demise of the kilogram.

Log in to reply

well, check out this -

www.youtube.com/watch?v=ZMByI4s-D-Y

Log in to reply

Ahh yes, the Veritasium video. I still think that he Sixty Symbols definition is much better.

Log in to reply

I edited the format of this note 4 times ( !!!!! ) so that it is well readable. And still doing improvements ! -_-

Log in to reply

No colors this time?

Log in to reply

Log in to reply

@Aditya Raut D'you know of a way by which we can invent colors on LaTeX?? For example there are 60 million colors and not all have LaTeX names, if we could use them somehow...

Log in to reply

How precisely can we find the mass of that platinum-iridium cylinder? :D

Log in to reply

Mmm. That Platinum-Iridium cylinder is made of the 2 most expensive elements.

Devious planLog in to reply

but someone told me there are 11 fundamental quantities..... what about four you think...

Log in to reply

I don't know, there are 2 more

supplementaryqualities, the \(\textbf{plane angle}\) and the \(\textbf{solid angle}\). but they are not fundamental, they'resupplementary.Log in to reply

Thanks abt these important info

Log in to reply

Mass -kilogram dude need a perfect definition......

Log in to reply

I read somewhere that 1kg is defined as mass of 1cubic decimeter of water at 4°C

Log in to reply

That's the old definition.

Log in to reply

Ohhhhh okkk

Log in to reply

Yeah! They teach this at the +1 level.

Log in to reply

Kilogram should have a better definition. ..btw where did it come from...

Log in to reply

In the new ncert definition of luminous intensity is different

Log in to reply

@Aditya Raut I have read that luminous intensity is fundamental quantity. But I think it can be derived using other fundamental quantities. So it should not be fundamental. Even NCERT writes a note about Luminous Intensity.

Log in to reply