IEMDaily - Video Lecture Notes

Definition

Guidelines for writing the units

(1) The symbol for a unit, which is not named after a scientist, written in small letter. For example, symbol of metre is m, for second is s.
(2) The full name of the unit, irrespective of the fact whether it is named after a scientist or not, is always written with a lower initial letter. e.g., unit of mass is written as kilogram.
(3) A compound unit formed by multiplication of two or more units is written after putting a dot, cross or leaving a space between the two symbols. For example, the unit of torque is written as N.m.
(4) Negative power is used for compound units, which are formed by dividing one unit by the other.
(5) A unit in its short form is never written in plural. For example, 10 metres can not be written as 10 ms.
(6) To avoid powers of ten in the magnitude of a quantity, prefix can be used with its unit, But a unit must not written with more than one prefixes. For example,

1 \times 10^{9} W

should be written as

1 G W

and not

1 k M W

Definition

SI unit of length and identify its sub units

The S.I. unit of length is meter (m).
The 17th General Conference on Weights and Measures (CGPM), 1983 has defined the meter as:
"The meter is the length of the path traveled by light in vacuum during a time interval of

\frac{1}{299792458}

of a second."
Sub units of meter: (1) centimeter (cm), (2) millimeter (mm), (3) micrometer (

μ m

) or micron, (4) nanometer (nm)

Example

Metric and Non- metric unit for measurement of length

Metric Units for Length Measurement:

Meter	Centimeter	Millimeter	Kilometer
1	100	1000	0.001
100	10,000	1,00,000	0.1

Non-Metric Unit for Length Measurement

Inch	Foot	Yard	Chain
1	1/12	1/36	0.00126
2	0.166667	0.0555556	0.00252525

Definition

SI unit of mass and its sub units

The S.I. unit of mass is kilogram (kg).
The 3rd General Conference on Weights and Measures (CGPM), 1901 has defined the kilogram as:"The kilogram is the unit of mass; it is equal to the mass of the international prototype of kilogram (which is an artifact made up of platinum-iridium kept at specific conditions)."
Sub units of kilogram: (1) gram (g) (2) milligram (mg)

Definition

Non metric units of length

Non metric units of length:
(a) Bigger units: (1) Astronomical unit (2) Light Year (3) Parsec.
(b) Smaller Units: (1) Angstrom (2) Fermi

Definition

Non metric units of mass

The mass of atomic particles such as the proton, neutron, and electron expressed in a unit called the atomic mass unit (a.m..u.).
1 a.m.u. is

1 / 12

th the mass of one carbon-12 atom.
1 a.m.u. =

1.66 \times 10^{- 27}

Definition

Methods for measurement of very large distances

For measuring long distances such as distance of the moon or a planet from the earth, special methods are adopted,which are as follows:
1)Radio echo method.
2)Laser pulse method
3)Parallax method.

Example

Units for measurement of large distance

Astronomical Unit
Astronomical unit is the mean distance of the center of the sun from the centre of the earth.
1 Astronomical Unit (AU) =

1.496 \times 10^{11} m

Light year:
Light year is the distance traveled by light in one year in vacuum.
Distance travelled by light in one year in vacuum = Velocity of light

\times

1 year (in seconds)

= 3 \times 10^{8} \times 365.25 \times 24 \times 60 \times 60 = 9.467 \times 10^{15} m

.
Therefore , 1 light year

= 9.467 \times 10^{15} m

One parsec

= 3.26

light-years.

Definition

SI unit of time

The S.I. unit of time is second (s).
A second is defined as 1/86400 th part of a mean solar day. i.e.,
1 s = 1/86400

\times

one mean solar day

Definition

Identification of fundamental quantities

A fundamental unit is a unit adopted for measurement of a base quantity. A base quantity is one of a conventionally chosen subset of physical quantities, where no subset quantity can be expressed in terms of the others.