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systems of units and units in S.I. system (units of length (sub-units of…
systems of units and units in S.I. system
need of unit for measurement
measurement:
it is the process of comparison of the given physical quantity with the known standard quality of the same nature
unit:
it is the quality of a constant magnitude which is used to measure the magnitudes of other quantities of the same nature
choice of unit
kinds of unit
systems of unit
C.G.S. system (or french system)
F.P.S. system (or British system)
M.K.S. system (or metric system)
Systeme Internationale d'Unites (or S.I. system)
use prefix with a unit
used for big measurements
deca
-da-10^1
hecto
-h-10^2
kilo
-k-10^3
mega
-M-10^6
giga
-G-10^9
tera
-T-10^12
peta
-P-10^15
exa
-E-10^18
zetta
-Z-10^21
yotta
-Y-10^24
used for small measurements
femto
-f-10^-15
atto
-a-10^-18
zepto
-z-10^-21
yoeto
-y-10^-24
pico
-p-10^-12
nano
-n-10^-9
micro
- -10^-6
milli
-m-10^-3
centi
-c-10^-2
deci
-d-10^-1
Fundamental quantities,units
and symbols in S.I. system:
Length
-metre-m
Mass
-kilogram-kg
Temperature
-kelvin-K
Time
-second-s
Luminous intensity
-Candela-cd
Electric Current-
ampere-A
Amount of substance
-mole-mol*
Angle
-radian-rd
Solid angle
-steradian-st-rd
units of length
S.I. unit of length
metre
sub-units of metre
micrometre\micron ()
= 10^-6m = 10^-4cm = 10^-3mm
millimetre (mm)
= 1/1000m = 10^-3 = 1/10cm
nanometre (nm)
= 1nm = 10^-9
centimetre (cm)
= 1/100m = 10^-2m
multiple units of metre
kilometre (km):
1000m (or 10^3 m)
non-metric units of length
bigger units (for measurement of distance
between two heavenly bodies)
#
Light Year (ly):
a light year is the distance travelled by light in vacuum
in a year
1 light year = speed of light* time 1 year
= 3 . 10^8 ms^-1 . (365 . 24 . 60 . 60s)
= 9.46 . 10^15m =9.46 . 10^12km
light minute
= 3 . 10^8 m s^-1 . 60s
= 1.8 . 10^10 m
light second
= 3 . 10^8 m s^-1 . 1s
= 3 . 10^8 m
Parsec:
one parsec is the distance from where the semi major axis of orbit of earth (1 A.U.) subtends an angle of one second
parsec . 1 = 1 A.U.
or
1 parsec = 1.496 . 10^11m / (1/3600) . (pi/180)
=3.08 . 10^16m
=3.08 . 10^16/ 9.46 . 10^15 ly = 3.26ly
Astronomical Unit (A.U.):
one astronomical unit is equal to the mean
distance between the earth and the sun
1 A.U. = 1.496 * 10^11 metre
smaller units
#
Angstrom (A .on top):
it is used to express the wavelength of light, size and seperation between two molecules [or atoms], radius of orbit of electron, etc.
1 Angstrom = 10^-10 m
=10^-8 cm = 10^-1 nm
1 micron = 10,000 A.
1 nm = 10 A.
fermi (f)
1 fermi = 10^-15 m
commonly used smaller and
bigger units of length (table)
Units of mass
Sub units of kilogram
gram:
one-thousandth part of a kilogram
milligram:
one millionth (10^-6) part of a kilogram or
one-thousandth (10^-3) part of a gram
S.I. unit of mass
kilogram (kg)
Multiple units
of kilogram
Quintal:
one hundred times a kilogram
1 quintal = 100kg
Metric Tonne:
one thousand times a kilogram
1 metric tonne = 1000kg = 10 quintal
Non-metric units of mass
atomic mass unit (a.m.u) or
unified atomic mass unit (u):
1/12th the mass of one carbon-12 atom.
the mass of 6.02 . 10^26 atoms of carbon -12 is 12 kg
1 a.m.u (or u) = 1/12 . 12/6.02 . 10^26 kg
= 1.66 . 10^-27 kg
solar mass
:
used to measure mass of large heavenly bodies.
1 solar mass = 2 . 10^30 kg
Units of time
S.I. unit of time
second:
the time interval of 9,192,631,770 vibrations
of radiation corresponding to the transition between
two hyperfine levels of the ground state of the
cesium - 133 atom
Bigger units of time
day:
time taken by the earth to rotate once
on its own axis. duration of 24 hours/ 1440 min/ 86400 s
month:
Gregorian calendar has January, March, May, July, August, October, December each of 31 days; April, June, September, November each of 30 days and February of 28 days (29 days leap year). Approximately, a month is a duration of 30 days.
hour (h):
duration of 60 minutes/ 3600 secs
lunar month:
Hindu (Vikram and Shak) and Muslim (Hizri) calendars are based on the phases of moon as seen from the earth. In these calendars, one month is the duration of one lunar cycle, nearly 29.5 days. the period of 12 lunar months is 354.37 days
minute (min):
duration of 60 seconds
year:
the time in which the earth completes one
revolution around the sun, which is nearly 365 days/ 365 . 86400 s = 3.1536 . 10^7 s
leap year:
the year in which the month
of February is of 29 days
1 leap year = 366 days
A leap year is divisible by 4
the exceptions are the century years: 1800, 1900 etc. eg.:2100
but the years divisible by 400, will be leap years, eg.: 2000, 2400
decade:
it is of 10 years/
3.1536 . 10^8s
century:
it is of 100 years
it will consist of 24 years each of 366 days
and 76 years each of 365 days. Therefore, a century consists of 36524 days/3.16 . 10^9 s
millennium:
it is of 1000 years, i.e., 3.16 . 10^10 s
smaller units of time
microsecond ( s):
10^-6 s
millisecond (ms):
10^-3
shake (shake):
10^-8 s
nanosecond (ns):
10^-9 s
*ref to mol(1 mol+C30= 1 kg= 6.02 multiplied by 10^26 entities [i.e., atoms or molecules or ions])
history of a metre
History of kilogram
one solar day is the time taken by the earth to
complete one rotation on its own axis.
for
history of a second