Errors in Measurement


The uncertainity in the measurement of a physical quantity is
called error. It is the difference between the true value and the measured
value of the physical quantity. Errors may be classified into many
categories.
(i) Constant errors
It is the same error repeated every time in a series of observations.
Constant error is due to faulty calibration of the scale in the measuring
instrument. In order to minimise constant error, measurements are
made by different possible methods and the mean value so obtained is
regarded as the true value.
(ii) Systematic errors
These are errors which occur due to a certain pattern or system.
These errors can be minimised by identifying the source of error.
Instrumental errors, personal errors due to individual traits and errors
due to external sources are some of the systematic errors.
(iii) Gross errors
Gross errors arise due to one or more than one of the following
reasons.
(1) Improper setting of the instrument.
(2) Wrong recordings of the observation.
(3) Not taking into account sources of error and precautions.
(4) Usage of wrong values in the calculation.
Gross errros can be minimised only if the observer is very careful
in his observations and sincere in his approach.
(iv) Random errors
It is very common that repeated measurements of a quantity give
values which are slightly different from each other. These errors have
no set pattern and occur in a random manner. Hence they are called
random errors. They can be minimised by repeating the measurements
many times and taking the arithmetic mean of all the values as the
correct reading.

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