Physical Quantities, Units and Dimensions

8/12/2019 Physical Quantities, Units and Dimensions

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Physical quantities

1. A physical quantity is a quantity that can be measured, i.e. speed, length, etc.

2. A non-physical quantity is a quantity that cannot be measubeauty, loyalty, feelings...

3. A physical quantity consists of a numerical magnitude and

4. Physical quantities are classified into base quantities and dquantities.

Mass of a book = 2000 g

(physical quantity) (numerical magnitude) (unit)


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Base quantity Unit Symbol

Length Metre MMass Kilogram kgTime Second sTemperature Kelvin KCurrent Ampere AAmount ofsubstance

Mole molLuminosity Candela cd


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Prefix Symbol Multiplication factor

Yotta Y 1 x 1024

Zetta Z 1 x 1021

Exa E 1 x 1018

Peta P 1 x 1015

Tera T 1 x 1012

Giga G 1 x 109

Mega M 1 x 106

Kilo k 1 x 103

Hecto h 1 x 102

Deca da 1 x 101

Deci d 1 x 10-1

Centi c 1 x 10-2

Milli m 1 x 10-3

Micro 1 x 10-6

Nano n 1 x 10-9

Pico p 1 x 10-12

Femto f 1 x 10-15

Atto a 1 x 10-18

Zepto z 1 x 10-21

Yocto y 1 x 10-24

Young Zookeepe

That Giant Man

david cute mous

father and zomb


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1. If the mass of a wooden block is m kg and its temperature heat content in joules (J) is given by the formula, = c is the specific heat capacity. What is the unit of c?

Solution:, =

=

Derived unit of c =

=


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2. Gravitational force is given by =

where dan ar

masses of two objects whereas R is the separation between the twFind the derived units of G, the universal gravitational constant.

Solution:

, =

=G

=

Derived unit of G =

G =


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1.4 Unit consistency & conversions1) 0.03 m = _____ cm

2) 2 109s = ________ ns

3) 7200 = ____________

n


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4) 123 = ___________

5) 2.16 = ________


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a) 22 has two significant figures

22.3 has three significant figures.

b) With zeroes, the situation is more complicated:i) Zeroes placed before other figures are not significant; 0.0

two significant figures.

ii) Zeroes placed between other figures are always significant;has four significant figures.

iii) Zeroes placed after other figures but behind a decimal poisignificant; 7.90 has three significant figures.


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c) 8200 has how many significant figures?

Normally is 2.

But better if you can write as below:

(i)8.200 103has four significant figures

(ii) 8.20 103has three significant figures

(iii) 8.2 103has two significant figures


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1. How many significant figures does each of the following nuhave?

a) 1230 b) 0.012 c) 0.0120 d) 12.30 e) 1.23

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Physical Quantities, Units and Dimensions