Measurement is the comparison of an unknown quantity with a known standard quantity of the same kind. Another important thing is to identify a quantity that can be measured (known as physical quantity).
Generally, most of the measurements are based on physical
quantities like length, mass, time, temperature etc.,
In measuring a physical quantity one needs to have an idea of
its various units, their interrelationships and also the various devices used
for its measurements.
Physical quantity
1.
A
physical quantity is a quantity that can be measured.
2.
Physical
quantity is expressed by stating
i. Magnitude of the physical quantity.
ii. The unit employed. Therefore
Physical quantity = magnitude x unit.
Standard unit
In measuring a physical quantity one needs to have an idea of
its various units, their interrelationship and also the various devices used
for its measurement.
The unit plays an important role in the description of a
physical quantity. However, the unit used for a particular physical quantity is
person-dependent. Hence, they need to be specified and standardized to maintain
uniformity. Under this treaty, an International Bureau of Weights and Measures
was established. This Bureau situated at serves in Paris has specified
standards units, measured more accurately with advanced techniques of science.
Characteristics of
standard unit
a)
It
should be of convenient size.
b)
It
should not change concerning space and time.
c)
It
should be possible to define, without any doubt or ambiguity.
d)
It
should not be perishable.
e)
It
should be easily reproduced.
Types of physical
quantities
a Fundamental quantities
These quantities do not depend on
other physical quantities. Lengths, mass and time are fundamental quantities.
b Derived quantities
These quantities are defined in terms
of fundamental quantities. Area, density, and volume are derived quantities.
Types of units
a Fundamental unit
The units of fundamental quantities
are called fundamental units.
b Derived unit
The units of derived quantities are
called derived units.
Measurement of Length
Length, a fundamental quantity, is used to measure the
distance between two points in space. The SI unit of length is meter (m) and
its C.G.S unit is centimetre (cm).
The various units used to measure length are µ m, mm, cm, and km. Length can be measured using devices like
meter scale, vernier callipers, measuring tape etc.,
Using a ruler we can measure the smallest reading accurately up
to 1 mm i.e. least count of the ruler is 1 mm. The length of a rod can be measured
using a scale by keeping the scale in contact with the object.
Length of rod = y – x =
2.5 cm – 1 cm
Length of rod = 1.5 cm
In the case of a curved line, the length of the curved line is found
by using a thread ruler method or divider ruler method.
Similarly, the diameter of a uniform wire is found by winding
it over a pencil. The length of the wounded wire over the pencil is measured by a
scale. The measured length of the coil is then divided by the number of turns which
gives the diameter of the wire.
Diameter of the wire = Length of AB / Number of turns
Measurement of Area
Area is a derived quantity that is obtained by multiplying
the two measurements of a regular body. For example, the area of a rectangle is
calculated as the product of its length and breadth. The SI unit of area is m2
or square meters. The other units of area are cm2, mm2, km2
etc.,
The area of an irregular object can be calculated by drawing
the outline of its shape on graph paper. The number of complete squares is
calculated, next the squares greater than half are also counted as a square,
leaving the squares less than half. The sum of all the squares gives the area
of the leaf to be that many cm2.
Measurement of volume
Volume is the space occupied by an object. The SI unit of
volume is m3 or cubic meter. The other units of volume are cm3,
ml, l etc.
1 ml = 1 cm3
1 ml = 10-6 m3
1 l = 103 cm3 = 103 ml
1 l = 10-3 m3
The volume of regular bodies can be calculated by measuring the
dimensions necessary for the calculations. The volume of a cube is given by
(side) 3.
Volume of liquids
Measuring jar
It is graduated in ml from bottom to top and used to measure the required amount of liquid.
Measuring flask
It has one mark etched on the neck and the liquid of only volume
of its capacity can be measured.
Pipette
It is filled by sucking the liquid into it. It is used to
take up only a fixed amount of liquid.
Burette
It resembles a measuring jar with a pitch cock provided at
the bottom. It is used to take the desired amount of liquids.
Measurement of mass
Mass is the measure of matter contained in a body? Common
balance and physical balances are the most used devices used for measuring it.
SI unit of mass is
kilogram. Common balance is used to find the unknown mass of an object using known
standard masses.
Weight is the force with which the earth pulls a body towards
its centre. The weight of a body is not a constant quantity but depends upon
the acceleration due to gravity acting on the body.
The acceleration due to gravity is not the same at all the places
on the earth, but changes from place to place.
The weight is generally measured in kilogram–force or
gram–force with the help of a spring balance.
One kilogram-force is the force with which the earth attracts a mass of one kilogram.
Similarly, one gram force (gf) is the force with which the earth attracts a
mass of 1 g.
The SI unit of weight is Newton. The amount of force with the
earth attracts a mass of 1 g.
The SI unit of weight is Newton. The amount of force acting
on a body, when the earth pulls a mass 100 g (98.1 g to be exact) is equal to
one Newton.
Measurement of time
Time is the interval between two events. In our daily lives,
many events are observed like heartbeat, blinking of eyes, appearance of
comets etc. These events may be either periodic or may not be periodic.
In airlines and railways, a 24-hour clock system is used,
for example, 3:25 P.M. in the 12-hour clock system is written as 15 hours 25 minutes
in the 24-hour clock system.
Simple pendulum
Take a brass bob connect it to a thread of length 100 cm
and suspend it from the nail fixed to a wall and the arrangement is as shown.
The bob is pulled gently toward the left and on releasing the
bob swings towards B and C and then returns back to position A.
The motion of the bob from point A to C and back to point A is called one oscillation and the time taken to complete one oscillation is called period. If the period is 2 seconds then such a pendulum is called seconds pendulum.
Reviewed by knowledge people creators
on
September 28, 2021
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