1.03 measuring length and time -1
TRANSCRIPT
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1.03
UnderstandingMeasurement
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Physics is a science which involvesmeasurements of various physicalquantities.
Choosing an appropriate instrumentto measure a physical quantity is
important to ensure that themeasurement is accurate.
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Common Measuring Instrument
Measuring tape
Metre rule Vernier Callipers
Micrometer Screw Gauge
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Measuring Tape
Measuring length of several metres.Measuring the circumference of a
round object.
Accuracy up to 1 cm.
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Metre Rule
Measure lengths from a few cm to 1m.
Accuracy up to 0.1 cm. Precaution to be taken when using a ruler:
a) Ensure that the object is in contact
with the ruler.b) Avoid parallax errors.
c) Avoid zero errors.
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Vernier Callipers
Measure length of less than 10cm.Measure internal or external
diameter of round object and the
depth of a hole. Accuracy up to 0.01cm.
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MicrometerScrew Gauge
Measure small lengths ranging
between 0.10mm and 25.00mm.
Measure diameters of wires and
thickness of steel plates.
Accuracy up to 0.01mm.
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Parts and Functions
Inside jaws
To measure the internal diameter
of an object.
Outside jawsTo measure the external diameteror length of an object.
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Parts and Functions
Tail
To measure the depth of an object.
Screw clamp
Tighten up the vernier scale toensure that the reading does notchange while the scale is being read.
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Measuring the internaldiameter of a beaker
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Measuring the diameter of apendulum bob
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Measuring the depth of atest tube
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Steps
Read the mark on the main scale precedingthe 0 mark on the vernier scale.
Read the mark on the vernier scale that isexactly in line with any mark on the mainscale.
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Main scale = 4.50 cm
Vernier scale = 0.00 cm
Reading of vernier callipers= main scale + vernier scale
= 4.50 cm + 0.00 cm
= 4.50 cm
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Main scale = 2.40 cm
Vernier scale = 0.09 cm
Reading of vernier callipers= main scale + vernier scale
= 2.40 cm + 0.09 cm
= 2.49 cm
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Main scale = 3.80 cm
Vernier scale = 0.07 cm
Reading of vernier callipers= main scale + vernier scale
= 3.80 cm + 0.07 cm
= 3.87 cm
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Main scale = 12.50 cm
Vernier scale = 0.00 cm
Reading of vernier callipers= main scale + vernier scale
= 12.50 cm + 0.00 cm
= 12.50 cm
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Zero Errors
No zero error
Positive zero error
Negative zero error
Correct reading= Callipers reading Zero error
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No zero error
0 cm 1
0 105
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Positive zero error
0 cm 1
0 5 10
Zero error= + 0.02cm
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Negative zero error
0 cm 1
0 105
Zero error= -[0.10-0.09]
= - 0.01cm
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Parts and Functions
Lock
To ensure that the thimble does not
rotate while you take the reading.
Ratchet knob
Prevents over-tightening and exertingtoo much pressure on the object.
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Main scale = 8.50 mm
Thimble scale = 0.48 mm
Reading of micrometer screw gauge= main scale + thimble scale
= 8.50 mm + 0.48 mm
= 8.98 mm
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Main scale = 0.50 mm
Thimble scale = 0.40 mm
Reading of micrometer screw gauge= main scale + thimble scale
= 0.50 mm + 0.40 mm
= 0.90 mm
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Main scale = 2.00 mm
Thimble scale = 0.19 mm
Reading of micrometer screw gauge
= main scale + thimble scale
= 2.00 mm + 0.19 mm
= 2.19 mm
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Main scale = 8.50 mm
Thimble scale = 0.49 mm
Reading of micrometer screw gauge
= main scale + thimble scale
= 8.50 mm + 0.49 mm
= 8.99 mm
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Main scale = 3.00 mm
Thimble scale = 0.46 mm
Reading of micrometer screw gauge
= main scale + thimble scale
= 3.00 mm + 0.46 mm
= 3.46 mm
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No zero error
00
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Positive zero error
0
5
0
Zero error= + 0.02 mm
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Negative zero error
0
45
Zero error
= - 0.03 mm
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Consistency
Consistency of an instrument is theability of the instrument to
measure a quantity with little or nodeviation among measurements.
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A deviation is the difference betweenthe measured value and its mean valueor the average value.
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Accuracy
Accuracy of a measurement is howclose the measurement made is to
the actual value.
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Consistent and accurate
Consistent but notaccurate
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Not consistent and notaccurate
Not consistent butaccurate
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Sensitivity
Sensitivity of an instrument is itsability to detect a small change in
the quantity to be measured.
The smaller the change which can
be measured by an instrument, themore sensitive is the instrument.
Th iti it f i t t
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The sensitivity of some common instrumentsfor measuring length.
Instrument Smallest reading
Measuring tape 1cm
Metre rule 0.1cm
Vernier Callipers 0.01cm
Micrometer screwgauge
0.001cm
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Errors in Measurement
There are two main types of errors inmeasurements.
Systematic errors
Random errors
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Systematic Errors
Systematic errors are due to incorrectcalibration of instruments.
Another cause of systematic error isthe zero error.
Zero error is due to non-zero readingwhen the actual reading should be zero.
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Random Errors
Random errors arise from unknown andunpredictable variations in condition.
Random error occur due to
parallax error
natural error (e.g. change in wind) wrong technique
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Random Errors
Random errors can be minimised byrepeating the measurement several
times and taking the average ormean value of the readings.
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Parallax Errors
Parallax error is error in the readingdue to the position of the observerseye.
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