Physical quantities

This presentation by Hooria Shahzad is about physical quantites, SI units, prefixes and scientific notation.

1. PHYSICAL QUANTITIES A physical quantity is quantity which can be measured. For Example: length, mass, time, temperature, electric current, light intensity, volume and many others. A physical quantity is always measured of natural non-living objects. Physical quantities have numerical magnitude and unit. For Example: If the length of a student is 104cm, then 104 is its numerical magnitude and cm is the unit of measurement.

2. PHYSICAL QUANTITIES The another example of physical quantity is that when a grocer says that each sugar bag contains 5 kg, he is describing its numerical magnitude as well as the unit of measurement. It would be meaningless to state 5 or kg only. Physical quantities are of two types: BASE QUANTITIES DERIVED QUANTITIES

3. BASE QUANTITIES Base quantities are the quantities on the basis of which other quantities are expressed. There are seven base quantities which include length, mass, time, temperature, intensity of light and amount of a substance.

4. DERIVED QUANTITIES Derived quantities are the quantities which are expressed in terms of base quantities. These include area, volume, speed, force, work, energy, power, electric charge.

5. SI UNITS SI Units- International System of Units What is unit? Once a standard is set for quantity then it can be expressed in terms of that standard quantity. This standard quantity is called a unit. The eleventh General Conference on Weight and Measures held in Paris in 1960 adopted a world-wide system of measurements called International System of Units. The International System of Units is referred as SI.

6. BASE UNITS AND DERIVED UNITS The SI unit contains base units and derived units. BASE UNITS: The units that describe base quantities are called base units.

7. BASE UNITS AND DERIVED UNITS DERIVED UNITS: Derived units are the units used to measure derived quantities.

8. SI PREFIXES Prefixes are the words or letters which we add to the beginning of a word to make a new word. For example, the word ‘’unhappy” consists of the prefix “un” (which means not) combined with the stem word “unhappy” means “not happy”. SI units have advantage that their multiples and sub-multiples can be expressed in terms of prefixes.

9. TABLE OF PREFIXES

10. SI PREFIXES Note that the kilogram is the only SI unit with a prefix as part of its name and symbol. Because multiple prefixes may not be used, in the case of the kilogram the prefix names are used with the unit name "gram" and the prefix symbols are used with the unit symbol "g." With this exception, any SI prefix may be used with any SI unit, including the degree Celsius and its symbol °C.

11. SI PREFIXES MULTIPLES AND SUB-MULTIPLES OF LENGHT

12. SCIENTIFIC NOTATION Scientific notation is a way to write large or small numbers with some power of ten. Scientific notation has a number of useful properties and is commonly used in calculators, by scientists, mathematicians and engineers. For example, a number 62750 can be expressed as 62.758*10 3 or 6.275*10 4 or 0.6275*10 5 . A ll these are correct but the number that has one non-zero digit before the decimal e.g.6.275*10 4 preferable be taken as a standard form. Similarly the standard form of 0.00045 s is 4.5*10 -4 s.

13. P RESENTATION BY: HOORIA SHAHZAD STUDENT AT: BEACONHOUSE