Vernier callipers

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1.4 UNDERSTANDING

MEASUREMENTS

Students should be able to:

1. Measure physical quantities using appropriateinstruments.

2. Explain sensitivity.

3. Explain accuracy and consistency.4. Explain types of experimental error.

5. Use appropriate techniques to reduce errors.


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Measuring Instruments


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Estimation of Dimensions

Suitable instruments are required to make the

measurement;- more reliable,

- better accuracy,

- more consistency.


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Sensitivity

Definition: the capability of an instrumentto respond to physical stimuli or to registersmall physical amounts or differences.

A sensitive instrument can; Detect small changes in a quantity measured,

React very fast to the changes inmeasurements made.

Instrument with smaller divisions on thescale are more sensitive.


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Precision

Definision : the degree of uniformity or

reproducibility of the measurements.


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The Vernier Scales


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Introduction

The precision of length measurements maybe increased by using a device that uses asliding vernier scale.

Two such instruments that you will use tomeasure lengths of objects are: vernier callipers

micrometer screw gauge.

These instruments have: a main scale (in millimetres)

a sliding or rotating vernier scale.


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Explanation

In figure below, the vernier scale (below) is dividedinto 10 equal divisions.

Vernier scale reading is the mark on the vernierscale which exactly coincides with a mark on themain scale (0.7 mm).

The reading = 3.0 +0.7 = 3.7 mm.


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Reading = 15.0+0.8 = 15.8 mm


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The vernier calipers

Vernier calipers allows readings to the nearest 0.02mm.

This instrument may be used to measure outer dimensions of objects (using the main jaws),

inside dimensions (using the smaller jaws at the top),

depths (using the stem).


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Example

37mm 0.46mm 37.46mm+ =


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34 mm 0.60 mm 34.60mm+ =


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40mm 0.00mm 40.00 mm+ =


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Micrometer Screw Gauge

A screw with an accurately constant pitch (theamount by which the thimble moves forward or

backward for one complete revolution).

A pitch = 0.50 mm

2 full turns are required to close the jaws by 1.00 mm.

The rotating thimble is subdivided into 50 equal

divisions.

The thimble passes through a frame that carriesa millimetre scale graduated to 0.5 mm.

While doing the measurement, the manufacturer

recommends 3 cl icksof the ratchet before

taking the reading.


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Example

7mm 0.38 mm 7.38mm+ =


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7.5mm 0.22 mm 7.72mm+ =


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3 mm 0.46mm 3.46mm+ =


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3.5 mm 0.06mm 3.56mm+ =

Vernier callipers

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