PHYSICS NOTES CHAPTER MEASUREMENTS

MEASUREMENT

Meter

  Meter is the unit of length in S.I. System.   Meter is defined as "The distance between the two marks on a Platinum-Iridium bar kept at 0^OC in the   International Bureau of Weight and Measures in Paris."   One meter = 100 cm   One meter = 1000 mm

Kilogram

  Kilogram is the unit of mass in S.I. System.   "Kilogram is defined as the mass of a platinum cylinder placed in the International Bureau of Weight and   Measures in Paris."   One kilogram = 1000gram

Second

  Second is the unit of time in S.I. System.   A second is defined in terms of the time period of Cs-133 atoms.   i.e." one second is equal to 9,192,631,770 periods of vibrations of Cs¹³³ atoms."   60 seconds = one minute   3600 seconds = one hour

Least Count

  Minimum measurement that can be made by a measuring device is known as " LEAST COUNT'.

  Least count (vernier callipers) = minimum measurement on main scale / total number of divisions on                                                                                                               vernier scale

. Least count (screw gauge) = minimum measurement on main scale / total number of divisions on                                                                                                        circular scale

  Smaller is the magnitude of least count of a measuring instrument, more precise the measuring   instrument is.   A measuring instrument can not measure any thing whose dimensions are less than the magnitude of   least count.   Least Count of Vernier Callipers = 0.01 cm   Least Count of Micrometer Screw gauge = 0.001 cm

Zero Error

  It is a defect in a measuring device (Vernier Callipers & Screw Gauge).   When jaws of a Vernier Callipers or Screw Gauge are closed, zero of main scale must coincides with the   zero of vernier scale or circular scale in case of screw gauge.   If they do not coincide then it is said that a zero error is present in the instrument.

Types Of Zero Error

  Zero error may be positive or negative.   A positive zero error in the instrument shows a larger measurement than the actual measurement.   In order to get exact measurement, positive zero error is subtracted from the total reading. .   A negative zero error in the instrument shows a smaller measurement than the actual measurement.   In order to get exact measurement, negative zero error is added to the total reading.

Pitch

"Perpendicular distance between two consecutive threads of the screw gauge or spherometer is called PITCH."

Pitch = Distance traveled on main scale / total number of rotations

Error

An error is defined as "The difference between the measured value and actual value."

  If two persons use the same instrument for measurement for finding the same measurement, it is not   essential that they may get the same results. There may arises a difference between their   measurements. This difference is referred to as an "ERROR".

Types Of Error

  Errors can be divided into three categories:   (1) Personal Error   (2) Systematic Error   (3) Random Error

Personal Error

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  An error comes into play because of faulty procedure adopted by by the observer is called "PERSONAL   ERROR".   Personal error comes into existence due to making an error in reading a scale. It is due to faulty   procedure adopted by the person making measurement.

Systematic Error

  The type of error arises due to defect in the measuring device is known as "SYSTEMATIC ERROR".   Generally it is called "ZERO ERROR". it may be positive or negative error. Systematic error can be   removed by correcting measurement device.

Random Error

  The error produced due to sudden change in experimental conditions is called "RANDOM ERROR".   For example:   Sudden change in temperature, change in humidity, fluctuation in potential difference (voltage).   It is an accidental error and is beyond the control of the person making measurement.