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.

4. Branches
of Physics

5. 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.

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

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

8. 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 m2.
• Temperature of a room is 300 K

9. 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.

10. 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

11. • 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

12. 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.

13. 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.

14. 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.

15. 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

17. 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
• Coulomb

18. 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

19. 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

20. 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
• 10kg
• 5N
• 15m

21. 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

22. 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.

23. 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.

24. SI prefixes
Factor Name Symbol Factor Name Symbol
1024 yotta Y 10−1 deci d
1021 zetta Z 10−2 centi c
1018 exa E 10−3 milli m
1015 peta P 10−6 micro μ
1012 tera T 10−9 nano n
109 giga G 10−12 pico p
106 mega M 10−15 femto f
103 kilo k 10−18 atto a
102 hecto h 10−21 zepto z
101 deka da 10−24 yocto y

25. • 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 103 m
• 7 megawatt = 7 MW = 7 x 106 W
Use of SI prefixes

26. 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.

27. 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

28. 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.