Tutorial
4 Fundamental and Derived Units
We have discussed about units in the last tutorial. By now we
know that units are further divided into fundamental units and derived units.
 |
| Fundamental and derived units |
Fundamental
Units:
Fundamental units are a group or a set of units of the given
physical quantities from which other units can be generated. Or otherwise they
can defined as that these units can neither be derived from one another nor can
be resolved into any other units. They are independent. Fundamental units are
also called as base units. There are 7 units of physical quantities which are
defined as fundamental units by the international system of units. As I have
stated earlier that all my tutorial will be in SI units unless otherwise
stated. So the Fundamental units in SI units are as follows: (It should be
noted that the definitions in the given table are new definitions according to
the international standards. There is no need for remembering all the values in
the given table or definitions but I would suggest to remember everything
except definitions.)
Name
|
Symbol & Full Form
|
Measure
|
Current Definition
|
Dimensional Symbol
|
Length
|
m(Meter)
|
Length
|
The meter is the
length of the path travelled by light in vacuum during a time interval of
1 ⁄ 299792458 of a second
|
L
|
Kilogram
|
kg(Kilo Gram)
|
Mass
|
The kilogram is
the unit of mass; it is equal to the mass of the international prototype of
the kilogram
|
M
|
Second
|
s(Second)
|
Time
|
The second is the
duration of 9192631770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the
ground state of the cesium 133 atom.
|
T
|
Ampere
|
A(Ampere)
|
Electric
Current
|
The 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 newton per meter of length.
|
I
|
Kelvin
|
K(Kelvin)
|
Thermodynamic
temperature
|
The kelvin, unit
of thermodynamic temperature, is the fraction 1 ⁄ 273.16 of
the thermodynamic temperature of the triple point of water.
|
Θ
|
Mole
|
mol(Mole)
|
Amount of
substance
|
The mole is the
amount of substance of a system which contains as many elementary entities as
there are atoms in 0.012 kilogram of carbon 12; its symbol is 'mol.
|
N
|
Candela
|
cd(Candela)
|
Luminous
Intensity
|
The candela is the
luminous intensity, in a given direction, of a source that emits
monochromatic radiation of frequency 540×1012hertz and that has a radiant intensity
in that direction of 1/683 watt per steradian.
|
J
|
Derived
units:
The units which are derived from the fundamental units are
called as derived units. For example we know that Force is the product of
“Mass” and “Acceleration”. We know that that acceleration is equal to the ratio
of the distance travelled to the square of the time (Precise definition will be
given in the upcoming tutorials. For now just consider this.), so the units of
force in SI units can be written as
F = Mass(kg).Acceleration(meter/ second2)
Thus the units of force are the
It can be seen that the units of force are product of one or
more base units. Thus it can be said that force is a derived quantity.
Some examples of other derived units in the real life can be
given as, voltage, Resistance, Magnetic induction, Velocity, Acceleration,
Volume, Area and many others come under derived quantity.
Some of the derived units which have specific names for their
derived unit are, plane angle(radian), solid angle(steradian), frequency(hertz),
force(newton), pressure,stress(pascal), energy, work, quantity of electricity(coulomb)
and others.
I think there is no need to remember these units except the base
units for now because you will get used to these units and automatically
remember them while you will complete learning all the tutorials.
Finally it should be remembered that this topic is very
important not only in real life but also for your exam as this is the basics
for the upcoming tutorials.
References:
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