Measurements in Science is the process of obtaining the magnitude of a physical quantity and expressing it relative to a certain basic, arbitrarily chosen, internationally accepted reference standard called UNIT.
We need only a limited number of units to express all the physical quantities because these quantities are dependent on each other. We assign a set for fundamental or base quantities only, the units for these are called the Fundamental/Base units.
All remaining quantities can be derived from the base quantities. The units for these derived quantities are called derived units.
A system of units = Fundamental Units + Derived Units
There are different systems of units e.g. CGS (centimeter, gram and second), MKS(meter, gram and second) etc. However, the most commonly used standard is the SI system.
SI System
7 Base quantities
| Base Quantity | Name | Symbol |
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric Current | ampere | A |
| Thermodynamics Temperature | Kelvin | K |
| Amount of substance | mole | mol |
| Luminous Intensity | candela | cd |
2 additional quantities
| Base Quantity | Name | Symbol |
| Plane Angle | radian | rad |
| Solid Angle | steradian | sr |
Errors
Degree of uncertainty associated with a measurement.
Result = measured value ± absolute error
Accuracy is a measure of how close the measured value is to the true value of a quantity.
Precision tells us to what resolution or limit the quantity is measured.
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