Types of Errors (Part - 5) - Units & Measurements Video Lecture - Class 11

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measurement part 5 is brought to you by
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please make sure that you have watched
unit and measurement part 1 - part 4
before proceeding with part 5 well now
that we have discussed the difference
between accuracy and precision of an
instrument let us discuss what is an
error any uncertainty in measurement of
a physical quantity is error what do we
mean to say when we say uncertainty in
measurement why do you think there would
be uncertainty in measurement let me
give you a very simple example to
understand why certain measurements are
uncertain it is not that all
measurements are uncertain see this
example let us suppose I asked you to
count the number of people present
inside a room you can just go and count
the number of heads and you can tell me
okay fine there are some 20 people
present in the room so there is no
question of uncertainty in the
measurement because if you have counted
it correctly the number has to be 20 but
if I ask you to count the number of
atoms in a room there is a big question
mark it is not easy for you to count the
exact number of atoms present in a room
so you might be doing certain
calculations and arriving at a value of
the number of atoms in a room now when
you do such calculations which involve
very big formulae as well as data you
tend to give approximate results and
factors where error comes into picture
so any uncertainty in measurement of a
physical quantity is either
classification of errors errors are
broadly classified into two types the
first is systematic errors and the
second is random error so we will
discuss each of them in detail
let us discuss systematic error the term
systematic it shows systematic means
something which is organized something
which happens very systematically
so systematically systematic errors tend
to shift the result in one direction
that means the actual result gets
shifted from its actual value in a
particular direction that is if the
value increases then it keeps increasing
if the value decreases it keeps
decreasing I know it might be confusing
at this point of time but once I discuss
the categories are the examples it will
be very clear to you now there are
certain causes of systematic errors now
the first causes instrumental errors
instrumental errors as the name suggests
is arises due to defect in the
instrument for example let us suppose if
the meter scale is worn off at the end
then what would happen
meet the scale we normally use meters in
to measure lens now suppose if it is
worn off at the end then obviously any
measurement which you take will not be
the exact value if you measure it five
centimeter with the metre scale it will
actually not be five centimeter because
you are unable to measure it accurately
from the end so in this case if you see
any measurement anywhere you take with
this meter scale will come out to be
something lesser than or greater than
the true value
now if the measured value comes out to
be something lesser than the value then
wherever you use this meter scale the
value will be lesser than that
so that is so this kind of errors are
systematic errors there is another
category that is imperfection in
experimental technique or procedure that
means the way you are measuring if there
is a defect in the way you are measuring
a physical quantity even that can give
rise to a systematic error for example
thermometer placed under the arm eight
measures lesser temperature than the
actual body temperature you must have
used thermometers when you fall in when
you have fever just try this out just
trying to keep the thermometer until
your armpit and take the temperature you
would find that the temperature measured
when kilometer is kept under the armpit
will differ from the temperature
measured when the thermometer is kept
inside your mouth now this difference
arises because this is a standard fact
that if you if this is the experimental
procedure you follow that is if you
place the thermometer and that armpit no
matter what their result will be lesser
than the actual value so this is also a
systematic error the third one is
personal errors personal error means
something which occurs due to your own
mistake for example reading a
thermometer from below the horizontal
line of sight if there is an error in
which you read the thermometer even in
that case you will get a value which
will be deviated from the actual right
now now let's see how systematic errors
shift the result in one direction in all
these three categories of errors if we
see that the value deviates from the
actual value in the single direction for
example take the first case that is the
meter scale won't go off at the end when
the meter scale is worn off any
measurement which you take will be
lesser than or greater than the true
value and this deviation will be uniform
throughout all the samples
similarly whoever the person may be and
wherever the place may be if the
thermometer is placed under armpit their
body temperature will always be lesser
than the true temperature similarly in
case of reading a thermometer
incorrectly 'whosoever temperature to
measure and wherever you measure the
value which you mentioned we'll all
these deviate in the same direction so
in all these three categories we see
that the errors shifts the result in one
particular direction so it is an
organized kind of shifting that is why
they are called systematic errors let us
now look at random error as the name
says random random means something that
happens have physically these are
irregular errors with respect to size
and sign that means they can cause
increase or decrease at any part of the
sample there is no uniformity in the
error at any means no consistent effects
across the entire sample that means some
way there might be a decrease from the
true value somewhere there going to be
an increase from the true value for
example let us say there is unexpected
fluctuations in voltage supply so in
that case you don't know whether this
will result in deviation of the actual
value it will be increase or decrease or
how it will be because the voltage
supply fluctuations are unexpected
anything can happen
similarly the temperature fluctuations
so when you are performing an experiment
wherein the voltage supply has to be
constant if there is a sudden change in
voltage supply you don't know how will
it affect the sample so these kind of
errors fall under kanga mirrors so let
us have a quick review systematic errors
means organized errors the errors it
shift the result in one direction random
error
irregular errors with respect to size
and sang thank you
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