Measurement in Science and Technology

Measurement is a process of comparing a physical quantity with a standard quantity. The standard quantity used to compare a physical quantity for its measurement is called unit. The internationally accepted modern system of units used in science is known as SI units.

In SI units there are 7 basic units. These are:

  1. metre for length
  2. kilogram for mass
  3. second for time
  4. Kelvin for temperature
  5. ampere for electric current
  6. candela for luminous intensity
  7. mole for amount of substances

The units obtained in terms of basic units are called derived units.

1. Rules while using SI prefixes

  1. No space is required between the prefix and the symbol of the unit.
  2. The prefixes are used only with the units and not alone.
  3. Use only one prefix at a time.
  4. SI prefix is not used with the unit °C.

2. Rules for Representing SI units

  1. While writing the value of physical quantity, the number and the unit are separated by a space.
  2. No space is given between number and °C, degree, minute and second of plane angle.
  3. The symbols of the unit are not changed while writing them in plural.
  4. The symbols of the units are not followed by a full stop except at the end of a sentence.
  5. In writing the SI unit obtained as a combination of unit a space is given between the symbols.
  6. When using powers with a unit name the modifier is used after the unit name.