of 23
8/3/2019 Understanding Measurements
1/23
UNDERSTANDINGMEASUREMENTS
Choosing appropriate instrument to measure
a physical quantity is important to ensure that
the measurement is accurate.
8/3/2019 Understanding Measurements
2/23
Common Measuring Instrument
Metre Ruler
-used to measure lengths ofa few centimetres to ametre.
-its accuracy is up to 0.1cm
Precaution to be taken when
using ruler-Make sure that the object isin contact with the ruler.
- Avoid parallax error
8/3/2019 Understanding Measurements
3/23
Vernier Callipers
Is used to measurelengths of less than10cm.
Also suitable formeasuring internalor external diameter
of round object. Accuracy is up to0.01cm
8/3/2019 Understanding Measurements
4/23
1 - Outside jaws: used to take external measures of objects 2 - Inside jaws: used to take internal measures of objects
3 - Depth probe: used to measure the depth of objects
4 - Main scale (cm)
5 - Main scale (inch)
6 - Vernier(cm)
7 - Vernier(inch)
8 - Retainer: used to block movable part
8/3/2019 Understanding Measurements
5/23
How to read
8/3/2019 Understanding Measurements
6/23
Figure 5: The reading is 34.60 mm
8/3/2019 Understanding Measurements
7/23
8/3/2019 Understanding Measurements
8/23
8/3/2019 Understanding Measurements
9/23
How to Use a Micrometer?
Turn the thimble until the object is gripped
gently between the anvil and spindle. Turn the ratchet knob until a "click" sound is
heard. This is to prevent exerting too muchpressure on the object measured.
Take the reading.
8/3/2019 Understanding Measurements
10/23
8/3/2019 Understanding Measurements
11/23
Figure 12: The reading is 7.72 mm.
8/3/2019 Understanding Measurements
12/23
What is the reading of the micrometerscrew gauge?
8/3/2019 Understanding Measurements
13/23
Ammeter & Voltmeter
Ammeters are measuringinstrument used to
measure electric current.
Voltmeters are measuring
instrument used to
measure potential
difference (voltage).
8/3/2019 Understanding Measurements
14/23
8/3/2019 Understanding Measurements
15/23
Difference between accuracy and
consistency
8/3/2019 Understanding Measurements
16/23
Sensitivity of Measuring
Instrument
The sensitivity of an instrument is its ability
to detect small changes in the quantity that
is being measured.
Measuring instruments that have smaller
scale parts are more sensitive.
8/3/2019 Understanding Measurements
17/23
INSTRUMENT SMALLEST READING
Measuring tape 1cm
Metre rule 0.1cm
Vernier callipers 0.01cm
Micrometer screw gauge 0.001cm
8/3/2019 Understanding Measurements
18/23
ERRORS IN MEASUREMENT
An error- is the difference between the
measured value and the actual
value
There are 2 types of error in measurement
a) systematic errorsb) random errors
8/3/2019 Understanding Measurements
19/23
Examples of systematic errors are
zero error, which cause by an incorrect position ofthe zero point,
an incorrect calibration of the measuringinstrument.
consistently improper use of equipment.
Systematic error can be reduced by
Conducting t
he experiment wit
hcare.
Repeating the experiment by using differentinstruments.
8/3/2019 Understanding Measurements
20/23
Zero Error
A zero error arises when the measuringinstrument does not start from exactly zero.
Zero errors are consistently present in everyreading of a measurement.
Th
ez
ero error can be positive or negative.
8/3/2019 Understanding Measurements
21/23
Random Error
Random error can cause by
personal errors such as human limitations of sight andtouch.
lack of sensitivity of the instrument: the instrument failto respond to the small change.
natural errors such as changes in temperature or wind,while the experiment is in progress.
wrong technique of measurement.
e.g parallax error.
Random error can be reduced by
taking repeat readings
find the average value of the reading.
8/3/2019 Understanding Measurements
22/23
Parallax Error
A parallax error is anerror in reading an
instrument due to the
eye of the observer
and pointer are not in a
line perpendicular to
the plane of the scale.
8/3/2019 Understanding Measurements
23/23
