FUNDAMENTAL PHYSICAL QUANTITIES AN

LENGTH AND TIME

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 Length

 Mass

 Time

The value of a physical quantity is written as a number (numeral) followed by a suitable unit. In Physics, we adopt the Standard International (SI) unit. Physical Quantity SI Unit Symbol

Length

Metre

m

Mass

Kilogram

kg

Time

Second

s

MEASUREMENT OF LENGTH

Length can be measured using a variety of instruments (tapes, rulers, vernier callipers and micrometer screw gauge) taking into account the different range of lengths to be measured and the accuracy of a measuring instrument.

Accuracy of a measuring instrument is the smallest possible measurement that we can make using the instrument without estimation. Alternatively, it can be defined as the smallest possible division we can read from the scale of the instrument.

An instrument with a smaller accuracy is more accurate than an instrument with a larger accuracy. Length Example Instrument Used Accuracy

Very short length

Diameter of a metal wire

Micrometer screw gauge

0.01 mm

Short length

Diameter of a test tube

Vernier callipers

0.01 cm

Medium length

Width of a student desk

Metre rule

0.1 cm

Long length

Length of a classroom

Measuring tape

0.1 cm

RULERS AND TAPES

The correct way to read the scale of a ruler is shown below. The eye must be placed vertically above the mark on the scale.

This is to avoid parallax error (reading from wrong directions)

GENERALPOSSIBLE SOURCES OF ERRORS IN LENGTH MEASUREMENTS

 Wrong calibration of instrument – where scale is wrongly marked.

 Zero error - instrument is not reading exactly zero before making measurements.

 Human error – failure to read or interpret the printed scale correctly.POSSIBLE SOURCES OF ERRORS IN LENGTH MEASUREMENTS

 Wrong calibration of instrument – where scale is wrongly marked.

 Zero error - instrument is not reading exactly zero before making measurements.

 Human error – failure to read or interpret the printed scale correctly.POSSIBLE S