Unit And Measurement - Physics, IAS UPSC Notes | EduRev

General Science(Prelims) by IRS Divey Sethi

UPSC : Unit And Measurement - Physics, IAS UPSC Notes | EduRev

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Unit And Measurement

Unit

A unit is a particular physical quantity, defined and adopted by convention, with which other particular quantities of the same kind are compared to express their value.

THE INTERNATIONAL SYSTEM OF UNITS

In earlier time scientists of different countries were using different systems of units for measurement.

• In CGS system they were centimetre, gram and second respectively.

• In FPS system they were foot, pound and second respectively.

• In MKS system they were metre, kilogram and second respectively.

  • The system of units which is at present internationally accepted for measurement is the Système Internationale d’ abbreviated as SI.
  • The SI was developed and recommended by General Conference on Weights and Measures in 1971 for international usage in scientific, technical, industrial and commercial work.

 

Base Quantity 

Name 

Symbol 

length

meter

m

mass

kilogram

kg

time

second

s

electric current

ampere

A

temperature

kelvin 

K

amount of substance

mole

mol

luminous intensity

candela

cd 

 

Units of long distance

  • Light year = distance travelled by the light in one year = 1016m
  • Parsec (Parallactic second) is the distance corresponding to a parallax of one second of arc,
  • 1 Parsec = 3.26 light year


Name

deca-

hecto-

kilo-

mega-

giga-

tera-

peta-

exa-

zetta-

yotta-

Prefix

da

h

k

M

G

T

P

E

Z

Y

Factor

101 

102 

103 

106 

109 

1012 

1015 

1018 

1021 

1024 

 

 Units of long distance

  • Light year = distance travelled by the light in one year = 1016m
  • Parsec (Parallactic second) is the distance corresponding to a parallax of one second of arc,
  • 1 Parsec = 3.26 light year

Name

deca-

hecto-

kilo-

mega-

giga-

tera-

peta-

exa-

zetta-

yotta-

Prefix

da

h

k

M

G

T

P

E

Z

Y

Factor

101 

102 

103 

106 

109 

1012 

1015 

1018 

1021 

1024 

 

Unit of short distance

Name

deci-

centi-

milli-

micro-

nano-

pico-

femto-

atto-

zepto-

yocto-

Prefix

d

c

m

μ

n

p

f

a

z

y

Factor

10−1 

10−2 

10−3 

10−6 

10−9 

10−12 

10−15 

10−18 

10−21 

10−24 

 

Mass & Weight

  • Mass is defined as the amount of matter an object has. One of the qualities of mass is that it has inertia Mass is a measure of how much inertia an object shows.
  • The weight of an object on earth depends on the force of attraction (gravity) between the object and earth.
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