Measurement is the comparison of an unknown quantity with a known standard quantity of 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. But 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 with respect to 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, 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 centimeter (cm).

The various units used to measure length are µ m, mm, cm, km. Length can be measured using devices like meter scale, vernier calipers, measuring tape etc.,

Using a ruler we can measure the smallest reading accurately up to 1 mm i.e. least count of 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 case of a curved line the length of 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 wounded wire over pencil is measured by a scale. The measured length of coil is then divided by the number of turns which gives the diameter of 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 measurement 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 meter. 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 a graph paper. The number of complete squares are 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 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

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 required amount of liquid.

It has one mark etched on 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 desired amount of liquids.

Measurement of mass

Mass is the measure of matter contained in a body? Common balance, physical balances are the mostly used devices used for measuring it.

SI unit of mass is kilogram. Common balance is used to find 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 same at all the places on the earth, but changes from place to place.

The weight is generally measured in kilogram – force kgf() or gram – force (gf) with the help of a spring balance.

One kilogram force (kgf) 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 life, many events are observed like heart beat, blinking of eyes, appearance of comets etc. These events may be either periodic or may not be periodic.

In air lines and railways, a 24 hour clock system is used, for example 3:25 P.M. in 12 hour clock system is written as 15 hour 25 minutes in 24 hour clock system.

Simple pendulum

Take a brass bob and connect it to a thread of length 100 cm and suspend it from the nail fixed to a wall and arrangement is as shown.

The bob is pulled gently toward the left and on releasing the bob swings towards B and C and then return back to a position A.

The motion of the bob from the point A to C and back to the point A is called one oscillation and time taken to complete one oscillation is called time period. If time period is 2 second then such a pendulum is called seconds pendulum.

Some Useful Fundamental Measurement Techniques Reviewed by knowledge people creators on September 28, 2021 Rating: 5