3. At the end of this lesson, students should
be able to:
Read and use Micrometer screw gauge,
Vernier Calliper and meter rule .
Describe inaccuracy and errors in
measurement.
3/33
6. The Vernier Callipers
This instrument may be used to measure outer dimensions of objects (using the
main jaws), inside dimensions (using the smaller jaws at the top), and depths
(using the stem).
Vernier calipers can measure length with an accuracy of up to 0.01 cm.
VERNIER CALLIPERS
6/33
15. MICROMETER SCREW GAUGE
A micrometer allows a measurement of the size of a body. It is one of the most accurate
mechanical devices in common use.
The micrometer screw gauge can be used to measure very small lengths such as the
diameter of a wire or the thickness of a piece of paper as it can measure length
accurately up to 0.01 mm.
Figure 5: Micrometer Screw Gauge
MICROMETER SCREW GAUGE
A mirometer allows a measurement of the size of a body. It is one
of the most accurate mechanical devices in common use.
A micrometer screw gauge can measure length accurately up to 0.01
mm.
15/33
23. Consistency
The consistency of a measuring
instrument is its ability to register the
same reading when a measurement
is repeated.
A set of measurements are
consistent if all the values are close
to the mean value.
23/33
24. The consistency of a measuring instrument can be
improved by
eliminating parallax errors during measurement.
exercising greater care and effort when taking readings.
using an instrument which is not defective.
24/33
25. Accuracy
Examples of Precision and Accuracy:
Low Accuracy
High Precision
High Accuracy
Low Precision
High Accuracy
High Precision
Examples of Precision and Accuracy:
Low Accuracy
High Precision
High Accuracy
Low Precision
High Accuracy
High Precision
Examples of Precision and Accuracy:
Low Accuracy
High Precision
High Accuracy
Low Precision
High Accuracy
High Precision
Accuracy is the degree of how close a measured value is to the actual (true)
value.
Precision is how close the measured values are to each other.
25/33
26. Ways to improve the accuracy of a
measurement:
a) Repeated readings are taken and
the average value is calculated.
b) Avoid parallax errors.
c) Avoid zero errors.
d) Use measuring instruments with a
higher accuracy.
26/33
27. The sensitivity of a measuring instrument is its ability to respond quickly to a
small change in the value of a measurement.
Measuring
Instruments
Sensitivity
Metre rule 0.1 cm
Vernier callipers 0.01 cm
Micrometer
screw gauge
0.001 cm
Wrist watch 1 s
Analogue stopwatch 0.1 s
Digital stopwatch 0.01 s
Ammeter 0.1 A
Miliammeter 1 mA
Sensitivity
The smaller the minimum scale division, the more sensitive is the measuring
instrument.
27/33
28. The difference between the real value and the observed value.
ERROR
There are two main types of errors, that is
a) Systematics error
b) Random error
28/33
29. SYSTEMATIC ERROR
A systematic error is an error in reading the scale when a physical
quantity is being measured. It caused by the instrument, observer
and surroundings.
29/33
30. Causes of a systematic error:
a) A zero error occurs when the reading shown on the instrument is not
zero while the true reading is zero.
b) An error is caused when there is a flaw in the instrument. For example,
the edge of a ruler which is worn out causes an error in the measurement
of a length.
c) An error is caused by a wrong assumption.
d) Slow reaction when using an instrument causes an error. For example,
there may be a delay in pressing a stop watch.
e) An error caused by incorrect calibration of instruments.
30/33
31. RANDOM ERROR
1) A random error is an error is an error which occurs when
the observer is reading the scale on the measuring instrument.
2) A reading obtained when a random error occurs can be
bigger or smaller than the true value, a positive or negative
error may occur.
3) A random error can be reduced by taking the measurement
of a physical quantity more than once and finding the average
reading.
31/33
32. Examples of random errors are:
a)parallax error or error of measurement when a
reading is taken from unsuitable position relative
to the scale.
b)error in the reading of the scale.
c)error due to a change in temperature as the
experiment is being carried out.
32/33
