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Lesson 1 - Physical Quantities and Units

Keywords

pico (p), nano (n), micro(µ), milli (m), centi (c), kilo (k), mega (M), giga (G), tera (T); Mass (kg); Length (m); Volume (L); Time (s); Electric Current (A); Temperature (K); Intensity of light (Cd); amount of a substance (mol)

Objectives

You should:

(a) be able to explain that some physical quantities consist of a numerical magnitude and a unit;
(b) be able to use the correct unit for its physical quantity;
(c) know how the prefixes and their symbols indicate decimal sub-multiples or multiples of units;
(d) be able to make suitable estimates of physical quantities.

Units

In 1960, the Eleventh General Conference on Weights and Measures was held in Paris. They adopted a universal system of measurement units called Le Systeme International d'Unites (French), which is a revised version of the metric system. This International System, or SI, as it is commonly referred to, is used for commerce and Science around the world.

There are seven SI base units. Everything that is measurable, can be measured by these base units, or by units derived from these bases. The table below shows the bases, their international symbols, and what they are used to measure.

Quantity

Unit

Abbreviation

Mass

kilograms

kg

Length

meters

m

Time

seconds

s

Electric Current

ampere

A

Temperature

Kelvin, Celsius

K,C

Intensity of light

candela

cd

amount of a substance

mole

mol

Numerical prefixes

The following table shows the numerical prefixes that with the ones you must know shaded in.

Factor

Name

Symbol

1024

yotta

Y

1021

zetta

Z

1018

exa

E

1015

peta

P

1012

tera

T

109

giga

G

106

mega

M

103

kilo

k

102

hecto

h

101

deka

da

10-1

deci

d

10-2

centi

c

10-3

milli

m

10-6

micro

µ

10-9

nano

n

10-12

pico

p

10-15

femto

f

10-18

atto

a

10-21

zepto

z

10-24

yocto

y

 

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