Units and measurements - Basic SI units

SCIENCE AND PHYSICS, Need for measurement in physics, Physical Quantity, Seven fundamental units, Rules for writing SI units, THEORY OF ERRORS,

1. UNITS AND MEASUREMENTS Present by Bhagavathy P

2. SCIENCE AND PHYSICS The word ‘science’ has its root in the Latin verb scientia , meaning “ ‘knowing the truth’ The word ‘physics’ is derived from the Greek word “ Fusis ”, meaning nature. The study of nature and natural phenomena is dealt within physics. Hence physics is considered as the most basic of all sciences.

3. Branches of Physics

4. Need for measurement in physics To understand any phenomenon in physics we have to perform experiments. Experiments require measurements, and we measure several physical properties like length, mass, time, temperature, pressure etc. Experimental verification of laws & theories also needs measurement of physical properties.

5. Measurement in everyday life Measurement of mass Measurement of volume

6. Measurement in everyday life Measurement of length Measurement of temperature

7. Physical Quantity A physical property that can be measured and described by a number is called physical quantity. Examples: Mass of a person is 65 kg. Length of a table is 3 m. Area of a hall is 100 m 2 . Temperature of a room is 300 K

8. Types of Physical Quantities Physical quantities are classified into two types. They are fundamental and derived quantities . Fundamental or base quantities are quantities which cannot be expressed in terms of any other physical quantities. Quantities that can be expressed in terms of fundamental quantities are called derived quantities. For example, area, volume, velocity, acceleration, force, etc.

9. Units for measurement The standard used for the measurement of a physical quantity is called a unit. Examples: metre, foot, inch for length kilogram, pound for mass second, minute, hour for time fahrenheit, kelvin for temperature

10. This system was first introduced in France. It is also known as Gaussian system of units. It is based on centimeter, gram and second as the fundamental units of length, mass and time. CGS system of units

11. MKS system of units This system was also introduced in France. It is also known as French system of units. It is based on meter, kilogram and second as the fundamental units of length, mass and time.

12. FPS system of units This system was introduced in Britain. It is also known as British system of units. It is based on foot, pound and second as the fundamental units of length, mass and time.

13. International System of units (SI) In 1971, General Conference on Weight and Measures held its meeting and decided a system of units for international usage. This system is called international system of units and abbreviated as SI from its French name. The SI unit consists of seven fundamental units and two supplementary units.

14. Seven fundamental units FUNDAMENTAL QUANTITY SI UNIT SYMBOL Length metre m Mass kilogram kg Time second s Temperature kelvin K Electric current ampere A Luminous intensity candela cd Amount of substance mole mol

15. Rules for writing SI units 1 Full name of unit always starts with small letter even if named after a person. newton ampere coulomb not Newton Ampere C oulomb

16. Rules for writing SI units 2 Symbol for unit named after a scientist should be in capital letter. N for newton K for kelvin A for ampere C for coulomb

17. Rules for writing SI units 3 Symbols for all other units are written in small letters. m for meter s for second kg for kilogram cd for candela

18. Rules for writing SI units 4 One space is left between the last digit of numeral and the symbol of a unit. 10 kg 5 N 15 m not 1 kg 5N 15m

19. Rules for writing SI units 5 The units do not have plural forms. 6 metre 14 kg 20 second 18 kelvin not 6 metres 14 kgs 20 seconds 18 kelvins

20. Rules for writing SI units 6 Full stop should not be used after the units. 7 metre 12 N 25 kg not 7 metre. 12 N. 25 kg.

21. Rules for writing SI units 7 No space is used between the symbols for units. 4 Js 19 Nm 25 VA not 4 J s 19 N m. 25 V A.

22. SI prefixes Factor Name Symbol Factor Name Symbol 10 24 yotta Y 10 −1 deci d 10 21 zetta Z 10 −2 centi c 10 18 exa E 10 −3 milli m 10 15 peta P 10 −6 micro μ 10 12 tera T 10 −9 nano n 10 9 giga G 10 −12 pico p 10 6 mega M 10 −15 femto f 10 3 kilo k 10 −18 atto a 10 2 hecto h 10 −21 zepto z 10 1 deka da 10 −24 yocto y

23. 3 milliampere = 3 mA = 3 x 10 −3 A 5 microvolt = 5 μV = 5 x 10 −6 V 8 nanosecond = 8 ns = 8 x 10 −9 s 6 picometre = 6 pm = 6 x 10 −12 m 5 kilometre = 5 km = 5 x 10 3 m 7 megawatt = 7 MW = 7 x 10 6 W Use of SI prefixes

24. THEORY OF ERRORS The foundation of all experimental science and technology is measurement. The result obtained from any measurement will contain some uncertainty. Such an uncertainty is termed error.

25. Errors in Measurement The uncertainty in a measurement is called an error. systematic error Random error and gross error are the three possible errors. Systematic errors are reproducible inaccuracies that are consistently in the same direction. These occur often due to a problem that persists throughout the experiment. Instrumental errors Imperfections in experimental technique or procedure Personal errors Errors due to external causes

26. Random errors & Gross error Random errors may arise due to random and unpredictable variations in experimental conditions like pressure, temperature, voltage supply etc. The error caused due to the shear carelessness of an observer is called gross error. For example ( i ) Reading an instrument without setting it properly. (ii) Taking observations in a wrong manner without bothering about the sources of errors and the precautions. (iii) Recording wrong observations. (iv) Using wrong values of the observations in calculations.