Page 37 - Class-11-Physics-Part-1_Neat

UNITS AND MEASUREMENT 23

Table 2.5 Range and order of time intervals

closer to the true value) but less precision (its of a human body, a thermometer placed
resolution is only 0.1 cm), while the under the armpit will always give a
second measurement is less accurate but temperature lower than the actual value of
more precise. Thus every measurement is the body temperature. Other external
approximate due to errors in measurement. In conditions (such as changes in temperature,
general, the errors in measurement can be humidity, wind velocity, etc.) during the
broadly classified as (a) systematic errors and experiment may systematically affect the
(b) random errors. measurement.
(c) Personal errors that arise due to an
Systematic errors
individual’s bias, lack of proper setting of
The systematic errors are those errors that the apparatus or individual’s carelessness
tend to be in one direction, either positive or in taking observations without observing
negative. Some of the sources of systematic proper precautions, etc. For example, if you,
errors are : by habit, always hold your head a bit too far
(a) Instrumental errors that arise from the to the right while reading the position of a
errors due to imperfect design or calibration needle on the scale, you will introduce an
of the measuring instrument, zero error in error due to parallax.
the instrument, etc. For example, the Systematic errors can be minimised by
temperature graduations of a thermometer improving experimental techniques, selecting
may be inadequately calibrated (it may read better instruments and removing personal bias
104 °C at the boiling point of water at STP as far as possible. For a given set-up, these
whereas it should read 100 °C); in a vernier errors may be estimated to a certain extent and
callipers the zero mark of vernier scale may the necessary corrections may be applied to the
not coincide with the zero mark of the main readings.
scale, or simply an ordinary metre scale may
be worn off at one end. Random errors
(b) Imperfection in experimental technique The random errors are those errors, which occur
or procedure To determine the temperature irregularly and hence are random with respect

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