Introduction To Measurement

By Author: Pierce Brosnan
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Introduction to measurement:

A physical quantity can not be understood completely by a simple description of its properties. While describing a person, we call him short or tall or heavy or light. This will not give full description of the person. We must have quantitative measurement of his height or weight, i.e., the physical quantities. There is an immense need to measure relevant physical quantities to have a comprehensive understanding of related physical phenomena. Lord Kelvin felt that the knowledge of physical quantities accurately and express them in numbers. Without measurements there can be no development in physics. The experimental measurements are highly essential to verify the theoretical laws. In our daily life we use a number of physical quantities like length , time , area, volume , speed, velocity, acceleration, force temperature etc. For measuring a physical quantity, a standard reference of the same physical quantity is essential. This standard reference is called 'Unit'.

Introduction to Measurement:: Centimeter and meter

A unit of measurement of a physical quantity is ...
... the standard reference of the same physical quantity which is used for comparison of he given physical quantity. In any measurement of a physical quantity, the final result is expressed as a number followed by the unit. For example, the height of a person is 1.6 metres. Here 'metre' is the unit and his height is expressed as 1.6 times (a number) multiplied by the unit. It can also be expressed as 160 centimetres, where 'centimetre' is the unit. The smaller the unit, the greater is the number of times that unit is contained in the physical quantity. Hence depending on the situation, suitable units have to be used to measure the quantities. The unit must be accepted internationally. A standard unit should be consistent , reproducible, invariable and easily available for usage. The process of measurement of a physical quantity involves : (a) Selection of a unit (b) to find the number of times that unit is contained in the physical quantity.

Introduction to Measurement::Significant measures

As precise and accurate measurements of physical quantities are quite essential in the study of physical sciences, measurements forms the basic foundation of any scientific investigation. There will be certain amount of uncertainty inherent in the measurement of physical quantities by any instrument. This uncertainty is called the 'error' . Basing on measured values of the physical quantity, we make certain calculations like addition, subtraction, multiplication and division. For example, we divide the distance travelled by an object by the time taken to find the speed of the object. Such calculations will also contain the errors in the measurements.

Certain (minimum number of ) physical quantities like length, mass, time, ...etc , are taken as the fundamental (base) quantities and are represented by capital letters as L, M, T, ..etc. Any other physical quantity can be expressed as a product of different powers of these fundamental (base) quantities. In such an expression, the power of a fundamental (base) quantity is called the dimension of that physical quantity in that base. For example, velocity can be expressed as displacement / time = `(L)/(T)` = L1-1 . Hence, the dimensions of velocity are in 1 in length and -1 in time. T

As every measurement contains errors, the result of a measurement is to be reported in such a manner to indicate the precision of measurement. We report the result of the measurement in the form of a number along with units of the physical quantity concerned. The number should be such that it includes all the digits that are known reliably and in addition one more digit that is an estimation and is not quite certain or reliable. The reliable digits plus the uncertain digit are called the 'Significant digits' or 'Significant figures' .

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