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Measurement and Experimental techniques

Parallax Error Parallax Error Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi–angle of inclination between those two lines. Parallax error is an operational and personal error due to improper reading of quantities with naked eye of an analyst. Nearby objects have a larger parallax than more distant objects when observed from different positions, so parallax can be used to determine the long distances like distance between stars.

Learning Objectives

After completing the topic, the student will be able to:

  • Use a scientific notation, powers of ten, while writing numbers of very large and very small sizes compactly and memorize the SI prefixes of powers of ten.
  • Scale the derived units by applying decimal multiplying factors and convert the magnitudes of units into different systems of units by using conversion factors.
  • Classify the errors that occur during experiments, avoid and rectify the errors while doing an experiment.
  • Cross check whether you are accurate or precise by using your experimental data.
  • Measure the uncertainity in the experimental value.
  • Round off the calculated value by using significant figures.
  • Recognize the significance of physical constants such as Planck's constant (h), Boltzmann constant (k) etc.
SI units SI logo The International System of Units is abbreviated as SI from French name: Le Système International d'Unitès. SI unit is now the dominant system of units in science and engineering, although there is still some usage of older metric units.
SI units

The International System of Units, abbreviated as SI, was established in 1960 by the 11th General Conference on Weights and Measures (CGPM) as the modern metric system of measurement. The core of the SI is the seven base units for the physical quantities length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity. These base units are:

SI base units for physical quantities
Base quantity SI base unit Symbol
Length meter m
Mass kilogram kg
Time second s
Electric current ampere A
Thermodynamic temperature Kelvin K
Amount of substance mole mol
Luminous intensity candela cd

The above stated are the fundamental units of matter. There are certain derived units to measure all the macroscopic and microscopic properties of matter.

 The chemist do come across many conversion factors during calculations. Examples of conversion of units for some parameters in chemistry
Conversion factors of units

In chemistry, we come across many parameters like mass, volume, temperature, pressure, energy etc. All of them are expressed with their standard units. For example, mass is expressed in kilograms, volume in meter cube and so on, which are SI units. Along with SI units we can use metric units, which are milligrams for mass, milliliters for volume etc. So, in order to convert SI units to C.G.S. units or metric units we need a conversion factor. A conversion factor is a numerical factor, used to multiply or divide a quantity when converting from one system of units to another.

Let us now discuss the parameters, units and their conversion factors.

Powers of ten:
A scientific notation is needed while writing numbers of very large and very small sizes compactly. If the precision is not required this can be done by writing number and multiplied by a power of ten, sometimes written in the form a × 10b.

Consider the number one thousand. Its numeral is "1000". It can be written as 1 × 103. "Powers of 10" is a very useful way of writing down large or small numbers. Instead of having lots of zeros, you show how many powers of 10 you need to make that many zeros.

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