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The International System of Units (SI units)






The International System of Units (SI units)

The SI units has seven base units and all the other are derived from these seven base units and are called derived units
Base Physical quantity
Symbol
SI units
Length
l
Meter (m)
Mass
m
Kilogram(kg)
Time
t
Sec(s)
Temperature
T
Kelvin(K)
Electric current
I
Ampere(A)
Amount of Substance
N
Mole(M)
Luminous intensity
Iv
Candela(cd)

Speed, Volume, density can be derived from these base Units.Some Common Physical quantity and their derived units
Physical Quantity
Symbol
Name
Unit
Mass
m , M
kilogram
kg
Linear position
Length, Distance
Radius
x, r
l, d
R
meter
m
Time
t,
second
s
Area
A
-
m2
Volume
V
-
m3
Density

-
kg/m3
Linear velocity
v, u, c
-
m/s
Linear momentum
p
-
kg*m/s
Linear acceleration
a
-
m/s2
Force
F
newton
N=kg*m/s2
Impulse
I
-
N*s
Work
Energy
W
E
joule
J=N*m
Power
P
watt
W=J/s

SI Unit system allow the use of prefix to show multiples or sub multiple of units
Prefixes in SI system Multiple
Prefix
Symbol
10-12
pico
p
10-9
nano
n
10-6
micro
μ
10-3
milli
m
10-2
centi
c
10-1
deci
d
10
deca
da
102
hecto
h
103
kilo
k
106
mega
M
109
giga
G
1012
tera
T


Mass and Weight
Mass of a substance is the amount of matter present in it while weight is the force exerted by gravity on an object. The mass of a substance is constant whereas its weight may vary from one place to another due to change in gravity. The mass of a substance can be determined very accurately by using an analytical balance

Volume-- it has the units of (length)3. So volume has units of m3 or cm3.A common unit, litre (L) is not an SI unit, is used for measurement of volume of liquids. 1 L = 1000 mL, 1000 cm3 = 1 dm3

1 cm3
1mL
1000 mm3
1 Litre
1000mL
1000 cm3
1 m3
106cm3
1000 L
1 dm3
1000 cm3
1 L

Density: Density of a substance is its amount of mass per unit volume.
SI unit of density = SI unit of mass/SI unit of volume
= kg/m3.
This unit is quite large and a chemist often expresses density in g /cm3

Temperature--There are three common scales to measure temperature—°C (degree Celsius), °F (degree Fahrenheit) and K (kelvin). Here, K is the SI unit.
K = °C + 273.15
$F= \frac {9}{5} C + 32$
Note—Temperature below 0 °C (i.e. negative values) are possible in Celsius scale but in Kelvin scale, negative temperature is not possible.

Quiz Time

Question 1 Which is of these a base unit.
A. Newton
B. coulomb
C. kilogram
D. m/sec
Question 2 What is the unit of momentum?
A. kg metre sec
B. kg metre/sec
C. kg/metre.sec
D. None of the above
Question 3 which is the below stand for prefix nano
A. 10-9
B. 109
C. 10-6
D. 10-12
Question 4 100 L is equal to
A. 1 dm3
B. 1000 mL
C. 10000 cm3
D. .1 m3
Question 5 What is the unit of Luminous intensity?
A. Mole
B. Candela
C. Ampere/sec
D. kg m/sec
Question 6What is the equivalent of -5 0C in Fahrenheit
A. 41
B. 23
C. 0
D. 268



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