STANDARD FOR MEASUREMENT

These are fixed and unchanging parameters with which instruments are compared for calibration and marking off. This makes it possible for two scientists to have the same result for quantity measurement using different instrument.
(a)MEASUREMENT OF LENGTH
  Length is given as length of light wave emitted from the gas Krypton – 86 in a discharge tube. One meter is 1650763.73 wavelength of this light.
It means measurement of distance is in meter. Examples are;
Distance
Example
Instrument for measurement
Large
Playground
Tapes
Shorter
Reading table
Meter rule
Smaller
Diameter of a rod
Vernier Caliper
Micro
Diameter of a wire or
Thickness of a paper
Micrometer guage




(b)MEASUREMENT OF TIME
The idea of time involves all events that happen in nature. In the laboratory, time is measured by stop watch or a stop clock. Some stop watch can measures time to 0.1 seconds, while stop clocks are as accurate, having an accuracy between 0.2 seconds and 0.5 seconds. One second is the time for 9192631770 cycles of radiation from gaseous Caesium atoms.

(c)MEASUREMENT OF MASS

The mass of a body is a measure of the quantity of matter it contains.  Mass is measured in Schools with the help of Beam or Chemical balance, other types are lever balance, direct reading balance and dial spring balance. Mass is measured in kilogram. One kilogram is the mass of a certain Platinum Iridium alloy cylinder kept at in France.
MEASUREMENT OF VOLUME
Volume is one of derived quantities. It is measured in cubic meter (m3) or centimetre (cm3). In the laboratory, various instruments are used for measuring various substances depending on some properties like state, shape, solubility in solvent and so on.
(i)                 Volume of Rectangular block
The volume of a rectangular object is given as;
V = L x B x H
Where L= Length of the object.
           B= Breadth of the object.
           H= Height of the object.
(ii)               Volume of a sphere
We obtain the diameter (d) with a micrometer gauge and the volume is calculated as;
  V = ¾ π r3 where r = d/2
(iii)             Volume of a cylindrical wire
We measure the diameter at different point of the wire and calculate the mean diameter.
Then, Volume is given as;
V = π r3l or π (d/2)2l = π d2/4 l   
(iv)              Volume of liquids
This is usually measured in cubic centimeter (cm3) or milliliter using the following;
Cylinder, Measuring flask, Burette and Pipette.
(v)               Volume of irregular solid
The volume of an irregular solid (e.g. a glass stopper) is obtained by immersing it completely in a measuring cylinder containing a liquid in which the solid in insoluble. The volume of the liquid displaced gives the volume of the solid.
NOTE: In order to read correctly the volume a liquid in the measuring cylinder or beaker, the eye should be along the same horizontal line as the meniscus of the liquid. This is to avoid parallax error.  
DIMENSION S OF PHYSICAL QUANTITIES
Dimension denotes the physical nature of a quantity in Physics. It indicates how physical quantities are made up in terms of the S.I. base quantities. In other words the physical quantity is said to have been expressed in term of dimension if it is expressed in terms of the three fundamental units.
Example
Deduce the dimension of (i) Velocity (ii) Force (iii) Pressure.
Solution
(i)                 Velocity = displacement ÷ time; V = L/T; V = LT-1
(ii)               Force = mass x acceleration
Mass x Velocity/time
                  Mass x displacement/time/time
                  Mass x displacement/time x time
                  M x L ÷ T2
Force = MLT-2
(iii)             Pressure = Force/ Area
 = Dimension of force / Dimension of area
 = MLT-2 / L2
            Pressure = MLT-2L-2
            Pressure = MT-2L-1.

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