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.
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.
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
Gross errors arise due
to one or more than one of the following reasons.
(1) Improper setting of the instrument.
1. Wrong recordings of the observation.
2. Not taking into account sources of error and
3. 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.
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.
The most common way of expressing an error is
percentage error. If the accuracy in measuring a quantity x is ∆x, then the percentage error in x is given by ( ∆x
/ x ) 100%.