Measurements are a part of our lives. Everybody makes measurements of some kind or the other. However, the accuracy of measurement varies from case to case. Scientists at environmental laboratories check the amount of arsenic in water to determine if it is suitable for drinking. This amount should be less than 0.00005 gram per litre of water. This measurement has to be very precise as it would affect thousands of people living in a locality. For scientific purposes, measurements have to be very accurate, and the measured values have to be stated in a precise manner.
A very systematic procedure is needed to get precise information about the quantity being measured. Also, scientists all over the world need to express the results of their measurements using a uniform method so that they understand each other.
Units
Measurements are made to get information about a variety of quantities. Length is one such quantity. One may wish to measure the length of an ant, a bacterium, a table, a room, or the diameter of a tennis ball, the distance between the earth and the sun, etc. We say that length is a physical quantity. Volume, time, speed, heat, temperature, electric current, etc. are some other examples of physical quantities.
We need to define a unit for the measurement of each physical quantity.This means that we have to select a particular value (amount) of a physical quantity. Measurement of a given quantity involves finding out the number of times of the unit the given quantity is. When we state the result of a measurement, we give this number as well the unit.
SI Units
SI Units are the system of physical units based on the metre, kilogram, second, ampere, kelvin, candela, and mole, together with a set of prefixes to indicate multiplication or division by a power of ten.
Table of SI Units is as follows :
| Quantity | Unit | Symbol |
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Temperature | kelvin | K |
| Luminous intensity | candela | cd |
| Electric current | ampere | A |
| Amount of substance | mole | mol |
| Angle | radian | rd |
| Solid angle | steradian | st-rd |
0 Comments