1.4 understanding measurement

Chapter 1 Introduction to Physics1.4 Understanding Measurements

1.4 Understanding MeasurementsMeter Rule

1.4 Understanding MeasurementsMeter RuleTo measure length from 1 cm up to 1 m.Precautions to be taken when using a ruler:Ensure that the object is in contact with the ruler to avoid inaccurate readings.Avoid parallax error and zero error.A metre rule has sensitivity or accuracy of 1mm.

1.4 Understanding MeasurementsVernier Calipers

1.4 Understanding MeasurementsVernier CalipersUsed to measure an object with dimensions up to120 mm / 12 cm.Can be used to measure the thickness of a stack of papers, diameter of a beaker and the depth of a beaker.

1.4 Understanding MeasurementsVernier CalipersThe main scale is marked in divisions of 1 mm.The vernier scale is marked in divisions of 0.1 mm.The vernier calipers has an accuracy of 0.1 mm or 0.01 cm

1.4 Understanding MeasurementsVernier CalipersThe principle of Vernier CalipersThe vernier scale is divided into ten equal divisions.The length of this 10 divisions are equal to 0.9 cm.Hence 1 mark on the vernier scale is equal to 0.09cm

1.4 Understanding MeasurementsVernier CalipersHow to read the vernier calipers?1. To measure with a vernier calipers, slide the vernier scale along the main scale until the object is held firmly between the jaws of the caliper.

1.4 Understanding MeasurementsVernier CalipersHow to read the vernier calipers?2. Read the main scale before 0 mark on the vernier scale.

3. Take the vernier scale reading that lines up any main scale reading.

1.4 Understanding MeasurementsVernier CalipersHow to read the vernier calipers?

1.4 Understanding MeasurementsVernier CalipersHow to read the vernier calipers?the main scale reading = 3.4 cmthe vernier scale reading = 0.6 mm= 0.06 cm

Therefore the reading is = 3.4 cm + 0.06 cm= 3.46 cm


3.10 cm0.03 cm3.13 cm


8.50 cm0.06 cm8.56 cm


2.10 cm0.06 cm2.16 cm


0.20 cm0.04 cm0.24 cm

1.4 Understanding MeasurementsVernier CalipersPositive zero error

The positive zero error shown is +0.4 mm / +0.04cm

To eliminate the positive zero error, Correct reading = (caliper reading) (+ zero error) = 3.46 cm (+0.04 cm) = 3.42 cm

1.4 Understanding MeasurementsVernier CalipersNegative zero error

The negative zero error shown is -0.2 mm / -0.02cm

To eliminate the negative zero error, Correct reading = (caliper reading) (- zero error) = 3.46 cm (-0.02 cm) = 3.48 cm

1.4 Understanding MeasurementsMicrometer Screw Gauge

1.4 Understanding MeasurementsMicrometer Screw GaugeA micrometer screw gauge is used to measure very small thickness and diameters ranging between 0.10 mm up to 25.00 mm.

The micrometer screw gauge can be used to measure diameter of wires and thickness sheet of paper to an accuracy of 0.01 mm

1.4 Understanding MeasurementsMicrometer Screw GaugeThe micrometer scale comprises :Main scale marked on the sleeveThimble scale / vernier scale marked on the thimble

1.4 Understanding MeasurementsMicrometer Screw GaugeHow to read the micrometer screw gauge?1. The object that is to be measured is placed between the jaws.2.The thimble is turned until its jaw touches the object.3.The ratchet knob must be used to secure the object firmly between the jaws, otherwise the instrument could be damaged or give an inconsistent reading. The manufacturer recommends 3 clicks of the ratchet before taking the reading.

1.4 Understanding MeasurementsMicrometer Screw GaugeHow to read the micrometer screw gauge?4.Read the main scale marking just before the thimble.

5.Find the vernier scale marking where the horizontal reference line of the main scale is in line with the graduation mark on the thimble.

1.4 Understanding MeasurementsMicrometer Screw GaugeHow to read the micrometer screw gauge?

1.4 Understanding MeasurementsMicrometer Screw GaugeHow to read the micrometer screw gauge?

The main scale reading = 7.5 mmThe vernier scale reading = 0.38 mm

Therefore the reading = 7.5 mm + 0.38 mm = 7.88 mm

1.4 Understanding MeasurementsMicrometer Screw GaugeHow to read the micrometer screw gauge?5.0 mm0.24 mm5.74 mm

1.4 Understanding MeasurementsMicrometer Screw GaugeBefore we use the micrometer screw gauge, we need to check for zero error in order to obtain accurate readings.

When the jaws are fully closed and the 0 mark on the thimble scale is exactly in line with the horizontal reference line there is no zero error

1.4 Understanding MeasurementsWhen the horizontal reference line is on the positive side of the 0 mark on the thimble scale.

The positive zero error as shown is +0.04 mm

To eliminate the positive zero error, Correct reading = (micrometer reading) (+ zero error) = 7.88 mm (+0.04 mm) = 7.84 mm

Micrometer Screw GaugePositive zero error

1.4 Understanding MeasurementsWhen the horizontal reference line is below the 0 mark on the thimble scale.

The negative zero error as shown is -0.03 mm

To eliminate the positive zero error, Correct reading = (micrometer reading) (- zero error) = 7.88 mm (-0.03 mm) = 7.91mm

Micrometer Screw GaugeNegative zero error

1.4 Understanding MeasurementsPhysics fileThe reading for a Vernier Calipers is always recorded in cm with two decimal places.The reading for a Micrometer Screw Gauge is always recorded in mm with two decimal places.

Measuring instrumentSmallest scale divisionVernier Calipers0.01 cmMicrometer Screw Gauge0.01 mm

Parallax Error due to observer not reading the scale straight on

Zero Error the starting point of the pointer is not zero but some other valuesNegative zero errorPositive zero error

SensitivitySensitivity of a measuring instrument is defined as the capability of that instrument to respond to physical stimuli or to register small physical amounts or differences.

The more sensitive the instrument, the more difficult and time-consuming it is to use the instrument.

1.4 Understanding MeasurementsError in measurement

Random errorsSystematic errorsRandom errors are due to:Very small changes in the surroundingOutside disturbances which cannot be taken into accountLack of sensitivity of the measuring instrumentsSystematic errors are due to:Incorrect calibration of equipmentImproper use of equipmentForgetting to account for some effectsTo reduce random errors:Take many readings and find the mean valueThe mean value will then close to the true or correct valueTo reduce systematic errors:Use different instruments to measure the same quantityComparing the dataExampleParallax errorExampleZero error

1.4 Understanding MeasurementsPrecision and Accuracy

1.4 Understanding MeasurementsPrecision and AccuracyPrecision (Consistency) is the degree of uniformity or reproducibility of the measurementsAccuracy is the degree of closeness of the measurements to the true or accepted value.

1.4 understanding measurement

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