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Understanding Physics
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Base and derived quantities
There two types:
•Base quantities
•Derived quantities
A base quantity is physical quantity which cannot be defined in term of other physical quantity
A derived quantity is a physical quantity. produced from combination of base quantities.
• Physical quantities are related to one another by mathematical equations, for example:
• velocity = displacement / time.
• Some physical quantities are chosen as base quantities. Other physical quantities are obtained from the base quantities using the appropriate algebraic relationships and these are called derived quantities .
Physical QuantitySymbol for the Quantity
length l
mass m
time t
electric current I
thermodynamic temperature
T
luminous intensity Iv
amount of substance n
Base Quantity
BASE UNITS
Physical Quantity Name of Unit Symbol
length metre m
mass kilogram kg
time second s
electric current ampere A
temperature kelvin K
luminous intensity
candela cd
amount of substance
mole mol
SOME EXAMPLES OF DERIVED SI UNITS
Physical Quantity SI Unit Symbol
area square metre m2
volume cubic metre m3
densitykilogram per cubic metre
kg.m-3
speedmetre per second
m.s-1
accelerationmetre per second squared
m.s-2
concentrationmole per cubic metre
mol.m-3
SOME DERIVED SI UNITS WITH SPECIAL NAMES
Physical Quantity Name of Unit Symbol
energy joule J
force newton N
pressure pascal Pa
power watt W
electric charge coulomb C
electric potential difference
volt V
electric resistance ohm W
frequency hertz Hz
PREFIXES
• Prefixes are used to represent physical quantities which are very big or very small in SI units.
• Prefixes correspond to powers of 10
• Each prefix has a specific name
• The table show list of prefixes with its multiplication factor.
• Students are required to memorize all prefixes start from pico until the tera.
Prefixes
Prefixes SI PrefixesPrefixes Symbol Multiple
PicoNanoMicroMilliCentiDeciKiloMegaGigaTera
pnµmcdkMGT
x10-12
x10-9
x10-6
x10-3
x10-2
x10-1
x103
x106
x109
x1012
• The prefixes can be used with any base units
• They are multipliers of the base unit
• Examples:
– 1 mm = 10-3 m
– 1 mg = 10-3 gMemorise all this Prefixes !!!!
Convert single number to standard form
STEP
1.Copy the digit but not digit of zero
2.Place the decimal point after first digit
3.Multiply with a power of ten4.Find the exponent of ten
Given:4,750,000
4.75 (moved 6 decimal places)
answer: 4.75 X 106
The original number was greater than 1 so the exponent is positive.
Given:0.000789
7.89 (moved 4 decimal places)
answer:7.89 x 10-4
The original number was less than 1 so the exponent is
negative.
Examples:
• The height of Mount Everest = 8848 m. Convert the height of Mount Everest into standard form.
Answer : 8.848 X 103
Answer
a. 0.0093
b. 0.000002
c. 3,013,000,000
d. 12,000,000,000
e. 130,000,000,000,000
Convert single number to standard form
Single numberStandard Form
a. 0.0093 9.3x10-3
b. 0.000002 2.0x10-6
c. 3,013,000,000 3.013x109
d. 12,000,000,000 1.2x1010
e. 130,000,000,000,000 1.3x1014
• Move decimal point to right for positive exponent of 10.
• Move decimal point to left for negative exponent of 10.
To Change from Standard Form to
Single Number:
Examples:
Given: 5.024 x 103
answer: 5,024 (3 places to right)
Positive exponent move decimal to the right.
Given:1.015 x 10-8
(8 places to left)answer: 0.00000001015
Negative exponent move decimal to the left.
Answer
Standard form
a. 1.3x10-5
b. 9.43 x10-4
c. 3.423 x107
d. 3.23 x106
e. 6.003 x109
to Single number
Answer
Standard Form Single number
1.3 x10-5 0.000013
9.43 x10-4 0.000943
3.423 x107 34,230,000
3.23 x106 3,230,000
6.003 x109 6,003,000
Summary
To express a positive number greater than or equal 1 to 10 in the standard form the given number can be express as A x10n ,where n is positive
To express a positive number less than 1 in standard form, the given number can be express as A x10n , where n is negative
Express single number to standard form
To convert a number given in the form to single number, see whether n is positive or negative.
If n positive, shift the decimal point n places to the rightIf n negative, shift the decimal point n places to the left
Kena tahu cara tukar unit suatu kuantiti kepada unit yang lain
Misalnya, diketahui 1 kg = 103 g, 1 cm = 10-2 m. Ketumpatan aluminium adalah 2.70 g/cm3.
Express the density of Aluminum in kg/m3. 2.70 g/cm3 = 2.70 (10-3 kg)/(10-2 m)3
= 2.7 (10-3/ 10-6) kg/m3
=2.7 x 103 kg/m3
Unit Conversion
Example:
530pF is equal to?
Solution:
530 pF = 530 x 10-12 F
530 pF = 5.30 x 102 x 10-12
= 5.3 x 102+(-12)
= 5.3 x 10-10
Prefix p is equivalent to 10-12
So convert 530 into standard form
ab x ac = ab+c
Next example…..Q: Convert 100 cm3 to m3
Solution:
• we already know c = 10-2
• 100 x 10-2 m3 ( this answer is wrong)
• In this case:
cm3 = (cm)3
= (10-2m)3
= 10-6m3
100cm3 = 100 x 10-6m3
= 1x 10-4m3 (ni baru betul..)