1.2 Understanding Base and Derived Quantities

1.2 Understanding Base and Derived Quantities

1. A physical quantity is a property of nature. It can be in relation to phenomena, objects or substances. Examples of physical quantities are:

(i) energy of a radiation — energy is the quantity relating to the phenomenon of radiation

(ii) length of a field — length is the quantity relating to the object which is the field

(iii) density of a liquid — density is the quantity relating to the substance which is the liquid.

2. Scientific notation is used for expressing very large and very small numbers.

Example:

>3800 m = 3.8 x m

>0.000456 s= 4.56 x 10 s

3. Powers of ten can be expressed in terms of multiple and sub-multiple prefixes as shown below:

4. All physical quantities are associated with a magnitude, which is the number expressing the size of the physical quantity, and most of the physical quantities are associated with a unit.

For example, in the statement “50 metres’ ‘50’ is the magnitude and ‘metre’ is the unit.

5. SI units are a set of units agreed upon internationally by the 11th General Conference on Weights and Measures held in 1960.

6 Base quantities are a set of quantities which are independent of one another and any one of them cannot be expressed in terms of a combination of the others.

7 The five base quantities, their symbols, the corresponding SI units and symbols are:

8. Derived quantities are a combination by multiplication or division of one or more base quantities.