Units and measurements

 Units & measurements

    Units plays an important roll in physics.

    For example :-

        Your friend give a task to measure the length of the wire

    Ans:- The length of this wire is 10 meters

              Here 10 represents the length & meters the Units or dimension.

Lets goo to deep

Fundamental quantities.

    The physical quantities which are independent of other quantities are called fundamental quantities

Example:- mass, length, temperature, etc.,

Derived quantities.

    The physical quantities which are derived from fundamental quantities are called Derived quantities

Example:- area, velocity, viscosity, pressure, Force constant, etc.,

The SI unit of the system of units.

    In 1971,General conference of weights and measures introduced a logical and rationalized system of units known as international system of units, abbreviated as SI in all languages. In this system, there are seven fundamental quantities and two supplementary quantities.

Fundamental quantities and their units & symbols

The above table represents fundamental quantities & their units.

Now we see the supplementary quantities & their units.

Supplementary quantities and their units & symbols

Rules of writing unit

1. In writing the unit of any quantity, small letters must be used for symbol of unit. For example:- m, m/s, kg etc.,
2. Symbols are not followed by a full stop.
3. If any unit is named after a scientist, its initial letter of a symbol is to be capital. For example;- Newton-N, Watt-W, Kelvin-K
4. The full name of a unit always begins with a small letter even if it is named after a scientist. For example;- 12 N - 12 newtons, 100W - 100watts, 2A - 2ampere
5. Symbols do not take plural form.

Some practical units

There are some practical units which are simultaneously used with SI units.

1. 1 fermi=10-15 m

2. 1 nanometer(nm)= 10-9m

3. 1 angstrom(Å)= 10-10m

4. 1 micron(μm)=10-6.m

5. 1 light year=9.46✕1015m

6. 1 parsec=3.08✕1016m

7. 1 astronomical unit(AU)=1.496✕1011m

8. 1 amu = 1.66✕10-27m

9. 1 ton= 1000kg

10. 1 lunar month=27.3 days

11. 1 solar day=365.25 avg days (or) 366.25 sidereal days

12. 1 shake=10-8s

13. 1 day= 86,400 seconds

14. 1 hour =3600 seconds

15. 1minute=60 seconds

16. 10=60’

17. 1’=60”

18. 1 radian= 57016’

19. π radians=1800

20. 00.celsius=273.15 kelvin

Definition & history of SI units

• Meter (m):-

In the year 1983 the unit meter came into the SI unit. one(1) meter defines as the path travelled by light in vacuum in 1/29,97,92,458 of a second.

• Kilogram (kg);-

In the year 1889 the unit kilogram came into the SI unit. one(1) kilogram is the mass of prototype{a certain platinum-iridium cylinder} preserved at the international Bureau of weights and measures at severs, near Paris.

• Ampere (A):-

In the year 1946 the unit ampere came into SI unit. One ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2✕10-7.

• Kelvin (K):-

In the year 1954 the unit kelvin came into SI unit. When the General conference on Weights & Measures (CGPM). It is also called as absolute temperature means at 0°The atoms are also freeze. This is also done experimentally as per the definition of ℃ than in use. It is the base unit of thermodynamic temperature.

• Seconds( S (or) Sec):-

It is a unit of time. Which has a fixed numerical value of Cesium frequency ΔνCs The unperturbed ground state hyperfine transition frequency of Cesium 113 atom, to be 9,19,26,31,770 when expressed in the unit Hz, which is equal to s−1.

• Luminous Intensity (Cd):-

In 1946 the Unit Candela came into the SI unit. It is the brightness of the full radiator at the temperature of solidification of platinum is 60 new candles per square centimeter.

• Mole(mol):-

It is the unit of measuring the amount of substance. Mainly this unit is used in Chemistry. 1 Mole is equal to 6.02214076*1023 atoms/ Ions/ Molecules in a given substance.