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Notes on Measurement

Chapter 1 - Measurement

INTRODUCTION

Definition:
Measurement is the process of comparison of unknown physical quantity with known standard quantity of the same kind.
Quantities such as length, mass, time, temperature, area, speed, etc are called physical quantities as they can be measured. We us different physical quantities to measure like a scale to measure length, a watch to measure time, a beam-balance with standard weight to measure mass. So, measurement is great applicable as selling and buying goods, measuring raw materials in industries, etc .

Units
The unit of measurement is defined as the reference standard used for the measurement of the physical quantity.
It is important parts of physical quantity and sometime known it as unit of measurement. In the present context, people use same measuring devices and units to measures physical quantities all over the world. And the unit known as Standard Unit(SI).The unit of measurement which is accepted all over the world is known as Standard Unit.. It makes convenient in measuring all over the world.
Why SI units are used for the scientific measurement?


TYPES OF UNITS
  1. Fundamental Unit:
    Those units which are independent and cannot be derived from other unit is called Fundamental Unit. The units of the fundamental quantities are called fundamental unit. For example: length, mass, time etc.

  2. Derived Unit:
    Those units which are composed of the fundamental units and are originated from the products and ratios of the fundamental unit is called derived unit. These units belong to physical quantities that are derived from basic physical properties. For example: Velocity, which is compose by fundamental quantity meter and second.
    Try out any three examples of derived quantity with reason.

    S.N Physical Quantity Unit
    1. Length Meter(m)
    2. Mass Kilogram(kg)
    3. Time Second(s)
    4. Temperature Kelvin(K)
    5. Current Ampere(A)
    6. Luminous intensity Candela(cd)
    7. Amount Of Substances Mole(mol)

Relation of Physical Quantity and its Derived Unit
Important Formulas and Units. It is useful in almost all chapter of physics so study well.


Quantity       Formula      Derived Unit      Fundamental     
Unit involved     
area Length(l) × Breadth(b) meter × meter
m2
volume Length(l) ×Breadth(b) × Height(h) meter × meter × meter
m3
density mass / volume kilogram / meter3
kg/m3
acceleration change in velocity / time taken meter / (second × second)
m/s2
velocity total displacement / time taken meter / second
m/s
force mass × acceleration (kilogram × meter) × (second × second)
or, Newton
kgm/s2 or N
pressure force / area newton / meter2
kg/ms2
work force(f) × distance(d) newton × meter
kgm2/s2
or, J
power work(w) / time(t) joule / second or watt
kgm2/s
or, W
moment force(f) × distance(d) newton × meter
kgm2/s2
frequency 1 / second 1 / second or Hertz
S-1
or, Hz

Write any three derived and fundamental quantities use by you so far.

Difference between derived and fundamental quantity?

Fundamental Unit Derived Unit
1. It do not depends upon others units. 1. It depends upon others units.
2. Till now there are only 7 fundamental units. 2. Many derived unit can be made from those 7 fundamental units.
For example: meter(m), second(s), etc. For example: velocity(v), pascal(pa), etc.


Let's derive

1.Force is derived from fundamental quantity.
soln:
Force = mass × acceleration
Force = kg × m/s2
Hence it is the combination of one kg one meter and 2 second and is derived from fundamental so force is called derived quantity.
let's try yourself:
1. Pressure is a derived quantity, why?
2. Watt is a derived unit, why?


Some Important Conversion

For Measurement of Length
10mm = 1cm
10cm = 1dm
10dm = 1m
10m = 1dam
10dam = 1 km
For Measurement of mass
10mg = 1cg
10cg = 1dg
10dg = 1g
10g = 1dag
10dag = 1 hg
10hg = 1kg
100kg = 1 quintal
10 quintals = 1 metric ton
For Measurement of time
60s = 1m
60m = 1hr
24hr = 1day
7 days = 1 week
52weeks = 1 year
365 days = 1 year
12 months = 1 year
1 solar day = 24 hours
Convert: 555 hr. into s
              20gm in to quintal




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